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 $192.59   10.222%   $212.2765   $212.28   $212.30   $212.30  
  Purchase #2 $213.69   5.761%   $226.0007   $226.00   $226.00   $226.00  
  Purchase #3 $57.94   13.821%   $65.9479   $65.95   $65.95   $65.90  
  Purchase #4 $119.84   12.276%   $134.5516   $134.55   $134.55   $134.60  
  Purchase #5 $141.68   8.399%   $153.5797   $153.58   $153.60   $153.60  
  Purchase #6 $30.71   12.686%   $34.6059   $34.61   $34.60   $34.60  
  Purchase #7 $47.93   6.275%   $50.9376   $50.94   $50.95   $50.90  
  7 purchase totals = $804.38       $877.8999   $877.91   $877.95   $877.90