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 $125.98   12.113%   $141.24   $141.24   $141.25   $141.20  
  Purchase #2 $59.28   13.504%   $67.2852   $67.29   $67.30   $67.30  
  Purchase #3 $50.51   12.713%   $56.9313   $56.93   $56.95   $56.90  
  Purchase #4 $82.41   13.369%   $93.4274   $93.43   $93.45   $93.40  
  Purchase #5 $98.89   4.568%   $103.4073   $103.41   $103.40   $103.40  
  Purchase #6 $96.86   9.459%   $106.022   $106.02   $106.00   $106.00  
  Purchase #7 $206.81   9.262%   $225.9647   $225.96   $225.95   $226.00  
  7 purchase totals = $720.74       $794.2779   $794.28   $794.30   $794.20