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 $186.41   13.166%   $210.9527   $210.95   $210.95   $211.00  
  Purchase #2 $10.55   10.198%   $11.6259   $11.63   $11.65   $11.60  
  Purchase #3 $241.80   12.655%   $272.3998   $272.40   $272.40   $272.40  
  Purchase #4 $93.99   13.739%   $106.9033   $106.90   $106.90   $106.90  
  Purchase #5 $16.88   6.635%   $18   $18.00   $18.00   $18.00  
  Purchase #6 $109.48   13.594%   $124.3627   $124.36   $124.35   $124.40  
  Purchase #7 $106.46   4.357%   $111.0985   $111.10   $111.10   $111.10  
  7 purchase totals = $765.57       $855.3429   $855.34   $855.35   $855.40