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 $217.95   8.722%   $236.9596   $236.96   $236.95   $237.00  
  Purchase #2 $136.95   4.297%   $142.8347   $142.83   $142.85   $142.80  
  Purchase #3 $194.74   13.873%   $221.7563   $221.76   $221.75   $221.80  
  Purchase #4 $62.85   10.834%   $69.6592   $69.66   $69.65   $69.70  
  Purchase #5 $87.42   13.496%   $99.2182   $99.22   $99.20   $99.20  
  Purchase #6 $140.72   10.490%   $155.4815   $155.48   $155.50   $155.50  
  Purchase #7 $119.38   4.226%   $124.425   $124.43   $124.45   $124.40  
  7 purchase totals = $960.01       $1,050.3345   $1,050.34   $1,050.35   $1,050.40