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 $89.49   3.846%   $92.9318   $92.93   $92.95   $92.90  
  Purchase #2 $169.86   6.747%   $181.3205   $181.32   $181.30   $181.30  
  Purchase #3 $152.89   6.281%   $162.493   $162.49   $162.50   $162.50  
  Purchase #4 $16.74   6.472%   $17.8234   $17.82   $17.80   $17.80  
  Purchase #5 $125.61   8.548%   $136.3471   $136.35   $136.35   $136.30  
  Purchase #6 $45.76   4.792%   $47.9528   $47.95   $47.95   $48.00  
  Purchase #7 $209.80   6.512%   $223.4622   $223.46   $223.45   $223.50  
  7 purchase totals = $810.15       $862.3308   $862.32   $862.30   $862.30