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 $68.43   12.455%   $76.953   $76.95   $76.95   $77.00  
  Purchase #2 $83.51   11.683%   $93.2665   $93.27   $93.25   $93.30  
  Purchase #3 $13.81   5.176%   $14.5248   $14.52   $14.50   $14.50  
  Purchase #4 $22.56   10.111%   $24.841   $24.84   $24.85   $24.80  
  Purchase #5 $164.81   5.188%   $173.3603   $173.36   $173.35   $173.40  
  Purchase #6 $124.56   8.639%   $135.3207   $135.32   $135.30   $135.30  
  Purchase #7 $119.52   13.873%   $136.101   $136.10   $136.10   $136.10  
  7 purchase totals = $597.20       $654.3673   $654.36   $654.30   $654.40