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 $85.51   13.153%   $96.7571   $96.76   $96.75   $96.80  
  Purchase #2 $49.68   3.391%   $51.3646   $51.36   $51.35   $51.40  
  Purchase #3 $126.35   6.673%   $134.7813   $134.78   $134.80   $134.80  
  Purchase #4 $178.80   3.769%   $185.539   $185.54   $185.55   $185.50  
  Purchase #5 $83.86   12.649%   $94.4675   $94.47   $94.45   $94.50  
  Purchase #6 $28.36   3.680%   $29.4036   $29.40   $29.40   $29.40  
  Purchase #7 $203.51   13.766%   $231.5252   $231.53   $231.55   $231.50  
  7 purchase totals = $756.07       $823.8383   $823.84   $823.85   $823.90