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 $83.31   11.600%   $92.974   $92.97   $92.95   $93.00  
  Purchase #2 $199.40   4.181%   $207.7369   $207.74   $207.75   $207.70  
  Purchase #3 $49.44   4.849%   $51.8373   $51.84   $51.85   $51.80  
  Purchase #4 $236.38   13.722%   $268.8161   $268.82   $268.80   $268.80  
  Purchase #5 $16.40   7.361%   $17.6072   $17.61   $17.60   $17.60  
  Purchase #6 $162.52   10.132%   $178.9865   $178.99   $179.00   $179.00  
  Purchase #7 $185.31   5.733%   $195.9338   $195.93   $195.95   $195.90  
  7 purchase totals = $932.76       $1,013.8918   $1,013.90   $1,013.90   $1,013.80