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 $26.50   10.543%   $29.2939   $29.29   $29.30   $29.30  
  Purchase #2 $9.88   12.480%   $11.113   $11.11   $11.10   $11.10  
  Purchase #3 $77.46   7.853%   $83.5429   $83.54   $83.55   $83.50  
  Purchase #4 $84.64   11.845%   $94.6656   $94.67   $94.65   $94.70  
  Purchase #5 $249.79   3.178%   $257.7283   $257.73   $257.75   $257.70  
  Purchase #6 $60.70   5.361%   $63.9541   $63.95   $63.95   $64.00  
  Purchase #7 $175.61   3.485%   $181.73   $181.73   $181.75   $181.70  
  7 purchase totals = $684.58       $722.0278   $722.02   $722.05   $722.00