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 $195.96   10.435%   $216.4084   $216.41   $216.40   $216.40  
  Purchase #2 $37.28   9.449%   $40.8026   $40.80   $40.80   $40.80  
  Purchase #3 $199.57   13.403%   $226.3184   $226.32   $226.30   $226.30  
  Purchase #4 $75.45   4.706%   $79.0007   $79.00   $79.00   $79.00  
  Purchase #5 $42.80   6.407%   $45.5422   $45.54   $45.55   $45.50  
  Purchase #6 $85.54   13.668%   $97.2316   $97.23   $97.25   $97.20  
  Purchase #7 $206.55   3.438%   $213.6512   $213.65   $213.65   $213.70  
  7 purchase totals = $843.15       $918.9551   $918.95   $918.95   $918.90