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 $67.67   7.603%   $72.815   $72.82   $72.80   $72.80  
  Purchase #2 $234.78   13.556%   $266.6068   $266.61   $266.60   $266.60  
  Purchase #3 $205.73   11.624%   $229.6441   $229.64   $229.65   $229.60  
  Purchase #4 $15.64   6.565%   $16.6668   $16.67   $16.65   $16.70  
  Purchase #5 $95.70   8.378%   $103.7177   $103.72   $103.70   $103.70  
  Purchase #6 $58.84   13.761%   $66.937   $66.94   $66.95   $66.90  
  Purchase #7 $143.93   12.301%   $161.6348   $161.63   $161.65   $161.60  
  7 purchase totals = $822.29       $918.0222   $918.03   $918.00   $917.90