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 $56.73   5.789%   $60.0141   $60.01   $60.00   $60.00  
  Purchase #2 $196.26   9.857%   $215.6053   $215.61   $215.60   $215.60  
  Purchase #3 $21.71   6.538%   $23.1294   $23.13   $23.15   $23.10  
  Purchase #4 $183.56   12.629%   $206.7418   $206.74   $206.75   $206.70  
  Purchase #5 $54.40   11.850%   $60.8464   $60.85   $60.85   $60.80  
  Purchase #6 $60.60   10.305%   $66.8448   $66.84   $66.85   $66.80  
  Purchase #7 $173.46   10.507%   $191.6854   $191.69   $191.70   $191.70  
  7 purchase totals = $746.72       $824.8672   $824.87   $824.90   $824.70