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 $87.83   9.821%   $96.4558   $96.46   $96.45   $96.50  
  Purchase #2 $120.27   12.448%   $135.2412   $135.24   $135.25   $135.20  
  Purchase #3 $152.49   10.812%   $168.9772   $168.98   $169.00   $169.00  
  Purchase #4 $101.90   10.356%   $112.4528   $112.45   $112.45   $112.50  
  Purchase #5 $157.31   10.169%   $173.3069   $173.31   $173.30   $173.30  
  Purchase #6 $53.94   8.498%   $58.5238   $58.52   $58.50   $58.50  
  Purchase #7 $250.40   4.445%   $261.5303   $261.53   $261.55   $261.50  
  7 purchase totals = $924.14       $1,006.4880   $1,006.49   $1,006.50   $1,006.50