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 $85.41   8.435%   $92.6143   $92.61   $92.60   $92.60  
  Purchase #2 $114.35   7.132%   $122.5054   $122.51   $122.50   $122.50  
  Purchase #3 $63.80   3.424%   $65.9845   $65.98   $66.00   $66.00  
  Purchase #4 $48.76   6.575%   $51.966   $51.97   $51.95   $52.00  
  Purchase #5 $200.25   4.504%   $209.2693   $209.27   $209.25   $209.30  
  Purchase #6 $249.25   11.411%   $277.6919   $277.69   $277.70   $277.70  
  Purchase #7 $44.30   3.687%   $45.9333   $45.93   $45.95   $45.90  
  7 purchase totals = $806.12       $865.9647   $865.96   $865.95   $866.00