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 $86.69   10.363%   $95.6737   $95.67   $95.65   $95.70  
  Purchase #2 $139.87   5.800%   $147.9825   $147.98   $148.00   $148.00  
  Purchase #3 $131.50   3.815%   $136.5167   $136.52   $136.50   $136.50  
  Purchase #4 $242.80   5.175%   $255.3649   $255.36   $255.35   $255.40  
  Purchase #5 $135.85   11.198%   $151.0625   $151.06   $151.05   $151.10  
  Purchase #6 $74.90   12.103%   $83.9651   $83.97   $83.95   $84.00  
  Purchase #7 $69.65   10.150%   $76.7195   $76.72   $76.70   $76.70  
  7 purchase totals = $881.26       $947.2849   $947.28   $947.20   $947.40