Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $246.52   11.503%   $274.8772   $274.88   $274.90   $274.90  
  Purchase #2 $148.58   9.323%   $162.4321   $162.43   $162.45   $162.40  
  Purchase #3 $114.65   3.684%   $118.8737   $118.87   $118.85   $118.90  
  Purchase #4 $195.58   4.781%   $204.9307   $204.93   $204.95   $204.90  
  Purchase #5 $198.82   10.204%   $219.1076   $219.11   $219.10   $219.10  
  Purchase #6 $156.27   10.188%   $172.1908   $172.19   $172.20   $172.20  
  Purchase #7 $165.96   13.476%   $188.3248   $188.32   $188.30   $188.30  
  7 purchase totals = $1,226.38       $1,340.7369   $1,340.73   $1,340.75   $1,340.70