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 $86.27   12.257%   $96.8441   $96.84   $96.85   $96.80  
  Purchase #2 $231.84   10.313%   $255.7497   $255.75   $255.75   $255.70  
  Purchase #3 $142.61   4.477%   $148.9946   $148.99   $149.00   $149.00  
  Purchase #4 $208.48   3.335%   $215.4328   $215.43   $215.45   $215.40  
  Purchase #5 $88.96   10.631%   $98.4173   $98.42   $98.40   $98.40  
  Purchase #6 $232.55   7.405%   $249.7703   $249.77   $249.75   $249.80  
  Purchase #7 $195.67   3.336%   $202.1976   $202.20   $202.20   $202.20  
  7 purchase totals = $1,186.38       $1,267.4064   $1,267.40   $1,267.40   $1,267.30