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 $248.70   10.263%   $274.2241   $274.22   $274.20   $274.20  
  Purchase #2 $182.69   7.131%   $195.7176   $195.72   $195.70   $195.70  
  Purchase #3 $56.71   7.532%   $60.9814   $60.98   $61.00   $61.00  
  Purchase #4 $88.69   12.411%   $99.6973   $99.70   $99.70   $99.70  
  Purchase #5 $118.87   5.119%   $124.955   $124.96   $124.95   $125.00  
  Purchase #6 $216.95   3.220%   $223.9358   $223.94   $223.95   $223.90  
  Purchase #7 $205.51   5.302%   $216.4061   $216.41   $216.40   $216.40  
  7 purchase totals = $1,118.12       $1,195.9173   $1,195.93   $1,195.90   $1,195.90