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 $85.56   6.705%   $91.2968   $91.30   $91.30   $91.30  
  Purchase #2 $191.38   13.192%   $216.6268   $216.63   $216.65   $216.60  
  Purchase #3 $147.70   9.616%   $161.9028   $161.90   $161.90   $161.90  
  Purchase #4 $54.33   6.678%   $57.9582   $57.96   $57.95   $58.00  
  Purchase #5 $97.89   3.604%   $101.418   $101.42   $101.40   $101.40  
  Purchase #6 $168.45   9.427%   $184.3298   $184.33   $184.35   $184.30  
  Purchase #7 $141.76   8.757%   $154.1739   $154.17   $154.15   $154.20  
  7 purchase totals = $887.07       $967.7063   $967.71   $967.70   $967.70