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 $84.85   10.598%   $93.8424   $93.84   $93.85   $93.80  
  Purchase #2 $65.58   3.250%   $67.7114   $67.71   $67.70   $67.70  
  Purchase #3 $207.79   4.862%   $217.8927   $217.89   $217.90   $217.90  
  Purchase #4 $58.28   7.447%   $62.6201   $62.62   $62.60   $62.60  
  Purchase #5 $93.38   13.405%   $105.8976   $105.90   $105.90   $105.90  
  Purchase #6 $189.82   6.554%   $202.2608   $202.26   $202.25   $202.30  
  Purchase #7 $136.74   5.207%   $143.8601   $143.86   $143.85   $143.90  
  7 purchase totals = $836.44       $894.0851   $894.08   $894.05   $894.10