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 $61.29   8.297%   $66.3752   $66.38   $66.40   $66.40  
  Purchase #2 $207.80   5.212%   $218.6305   $218.63   $218.65   $218.60  
  Purchase #3 $107.63   10.295%   $118.7105   $118.71   $118.70   $118.70  
  Purchase #4 $26.55   3.796%   $27.5578   $27.56   $27.55   $27.60  
  Purchase #5 $177.39   12.341%   $199.2817   $199.28   $199.30   $199.30  
  Purchase #6 $97.54   9.194%   $106.5078   $106.51   $106.50   $106.50  
  Purchase #7 $118.68   5.323%   $124.9973   $125.00   $125.00   $125.00  
  7 purchase totals = $796.88       $862.0608   $862.07   $862.10   $862.10