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 $243.70   8.842%   $265.248   $265.25   $265.25   $265.20  
  Purchase #2 $23.95   13.205%   $27.1126   $27.11   $27.10   $27.10  
  Purchase #3 $10.56   10.833%   $11.704   $11.70   $11.70   $11.70  
  Purchase #4 $26.39   5.594%   $27.8663   $27.87   $27.85   $27.90  
  Purchase #5 $243.66   10.117%   $268.3111   $268.31   $268.30   $268.30  
  Purchase #6 $180.66   8.655%   $196.2961   $196.30   $196.30   $196.30  
  Purchase #7 $148.51   9.598%   $162.764   $162.76   $162.75   $162.80  
  7 purchase totals = $877.43       $959.3021   $959.30   $959.25   $959.30