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 $50.69   5.706%   $53.5824   $53.58   $53.60   $53.60  
  Purchase #2 $44.27   7.695%   $47.6766   $47.68   $47.70   $47.70  
  Purchase #3 $117.61   6.279%   $124.9947   $124.99   $125.00   $125.00  
  Purchase #4 $24.68   3.275%   $25.4883   $25.49   $25.50   $25.50  
  Purchase #5 $96.66   12.191%   $108.4438   $108.44   $108.45   $108.40  
  Purchase #6 $234.64   8.521%   $254.6337   $254.63   $254.65   $254.60  
  Purchase #7 $102.62   7.215%   $110.024   $110.02   $110.00   $110.00  
  7 purchase totals = $671.17       $724.8435   $724.83   $724.90   $724.80