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 $60.86   11.530%   $67.8772   $67.88   $67.90   $67.90  
  Purchase #2 $53.94   12.503%   $60.6841   $60.68   $60.70   $60.70  
  Purchase #3 $95.69   11.155%   $106.3642   $106.36   $106.35   $106.40  
  Purchase #4 $7.51   9.612%   $8.2319   $8.23   $8.25   $8.20  
  Purchase #5 $238.43   10.111%   $262.5377   $262.54   $262.55   $262.50  
  Purchase #6 $32.70   12.522%   $36.7947   $36.79   $36.80   $36.80  
  Purchase #7 $25.73   11.480%   $28.6838   $28.68   $28.70   $28.70  
  7 purchase totals = $514.86       $571.1736   $571.16   $571.25   $571.20