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 $36.49   13.653%   $41.472   $41.47   $41.45   $41.50  
  Purchase #2 $243.89   13.137%   $275.9298   $275.93   $275.95   $275.90  
  Purchase #3 $100.88   8.808%   $109.7655   $109.77   $109.75   $109.80  
  Purchase #4 $44.68   8.179%   $48.3344   $48.33   $48.35   $48.30  
  Purchase #5 $245.92   11.488%   $274.1713   $274.17   $274.15   $274.20  
  Purchase #6 $69.49   8.376%   $75.3105   $75.31   $75.30   $75.30  
  Purchase #7 $135.70   3.358%   $140.2568   $140.26   $140.25   $140.30  
  7 purchase totals = $877.05       $965.2403   $965.24   $965.20   $965.30