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 $217.32   11.217%   $241.6968   $241.70   $241.70   $241.70  
  Purchase #2 $239.79   7.153%   $256.9422   $256.94   $256.95   $256.90  
  Purchase #3 $40.83   8.528%   $44.312   $44.31   $44.30   $44.30  
  Purchase #4 $44.72   13.530%   $50.7706   $50.77   $50.75   $50.80  
  Purchase #5 $178.81   5.406%   $188.4765   $188.48   $188.50   $188.50  
  Purchase #6 $60.96   11.151%   $67.7576   $67.76   $67.75   $67.80  
  Purchase #7 $74.62   8.303%   $80.8157   $80.82   $80.80   $80.80  
  7 purchase totals = $857.05       $930.7714   $930.78   $930.75   $930.80