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 $54.63   9.865%   $60.0192   $60.02   $60.00   $60.00  
  Purchase #2 $227.98   13.645%   $259.0879   $259.09   $259.10   $259.10  
  Purchase #3 $53.89   8.421%   $58.4281   $58.43   $58.45   $58.40  
  Purchase #4 $23.62   9.745%   $25.9218   $25.92   $25.90   $25.90  
  Purchase #5 $149.88   5.715%   $158.4456   $158.45   $158.45   $158.40  
  Purchase #6 $88.43   7.232%   $94.8253   $94.83   $94.85   $94.80  
  Purchase #7 $95.73   10.408%   $105.6936   $105.69   $105.70   $105.70  
  7 purchase totals = $694.16       $762.4215   $762.43   $762.45   $762.30