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 $185.31   8.503%   $201.0669   $201.07   $201.05   $201.10  
  Purchase #2 $241.79   8.500%   $262.3422   $262.34   $262.35   $262.30  
  Purchase #3 $26.43   5.661%   $27.9262   $27.93   $27.95   $27.90  
  Purchase #4 $10.82   6.316%   $11.5034   $11.50   $11.50   $11.50  
  Purchase #5 $33.41   9.131%   $36.4607   $36.46   $36.45   $36.50  
  Purchase #6 $185.71   4.600%   $194.2527   $194.25   $194.25   $194.30  
  Purchase #7 $171.98   6.610%   $183.3479   $183.35   $183.35   $183.30  
  7 purchase totals = $855.45       $916.9000   $916.90   $916.90   $916.90