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 $60.71   13.594%   $68.9629   $68.96   $68.95   $69.00  
  Purchase #2 $43.82   13.174%   $49.5928   $49.59   $49.60   $49.60  
  Purchase #3 $39.35   12.488%   $44.264   $44.26   $44.25   $44.30  
  Purchase #4 $56.78   13.365%   $64.3686   $64.37   $64.35   $64.40  
  Purchase #5 $84.77   4.166%   $88.3015   $88.30   $88.30   $88.30  
  Purchase #6 $36.92   8.765%   $40.156   $40.16   $40.15   $40.20  
  Purchase #7 $7.53   7.180%   $8.0707   $8.07   $8.05   $8.10  
  7 purchase totals = $329.88       $363.7165   $363.71   $363.65   $363.90