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 $68.77   7.223%   $73.7373   $73.74   $73.75   $73.70  
  Purchase #2 $90.88   13.269%   $102.9389   $102.94   $102.95   $102.90  
  Purchase #3 $246.62   12.300%   $276.9543   $276.95   $276.95   $277.00  
  Purchase #4 $93.69   3.578%   $97.0422   $97.04   $97.05   $97.00  
  Purchase #5 $173.98   7.345%   $186.7588   $186.76   $186.75   $186.80  
  Purchase #6 $126.84   13.765%   $144.2995   $144.30   $144.30   $144.30  
  Purchase #7 $60.88   10.760%   $67.4307   $67.43   $67.45   $67.40  
  7 purchase totals = $861.66       $949.1617   $949.16   $949.20   $949.10