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 $10.67   3.181%   $11.0094   $11.01   $11.00   $11.00  
  Purchase #2 $185.28   5.311%   $195.1202   $195.12   $195.10   $195.10  
  Purchase #3 $18.42   12.125%   $20.6534   $20.65   $20.65   $20.70  
  Purchase #4 $135.65   8.139%   $146.6906   $146.69   $146.70   $146.70  
  Purchase #5 $134.51   3.831%   $139.6631   $139.66   $139.65   $139.70  
  Purchase #6 $27.85   3.317%   $28.7738   $28.77   $28.75   $28.80  
  Purchase #7 $250.28   5.223%   $263.3521   $263.35   $263.35   $263.40  
  7 purchase totals = $762.66       $805.2626   $805.25   $805.20   $805.40