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 $63.79   3.401%   $65.9595   $65.96   $65.95   $66.00  
  Purchase #2 $115.69   9.380%   $126.5417   $126.54   $126.55   $126.50  
  Purchase #3 $186.71   6.534%   $198.9096   $198.91   $198.90   $198.90  
  Purchase #4 $115.58   7.145%   $123.8382   $123.84   $123.85   $123.80  
  Purchase #5 $63.28   9.807%   $69.4859   $69.49   $69.50   $69.50  
  Purchase #6 $33.38   8.418%   $36.1899   $36.19   $36.20   $36.20  
  Purchase #7 $121.53   6.218%   $129.0867   $129.09   $129.10   $129.10  
  7 purchase totals = $699.96       $750.0115   $750.02   $750.05   $750.00