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 $68.79   10.382%   $75.9318   $75.93   $75.95   $75.90  
  Purchase #2 $119.89   12.766%   $135.1952   $135.20   $135.20   $135.20  
  Purchase #3 $25.61   6.458%   $27.2639   $27.26   $27.25   $27.30  
  Purchase #4 $89.91   7.398%   $96.5615   $96.56   $96.55   $96.60  
  Purchase #5 $87.60   11.853%   $97.9832   $97.98   $98.00   $98.00  
  Purchase #6 $17.73   13.466%   $20.1175   $20.12   $20.10   $20.10  
  Purchase #7 $14.87   11.809%   $16.626   $16.63   $16.65   $16.60  
  7 purchase totals = $424.40       $469.6791   $469.68   $469.70   $469.70