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 $239.37   9.517%   $262.1508   $262.15   $262.15   $262.20  
  Purchase #2 $212.87   8.441%   $230.8384   $230.84   $230.85   $230.80  
  Purchase #3 $182.55   13.342%   $206.9058   $206.91   $206.90   $206.90  
  Purchase #4 $149.36   7.579%   $160.68   $160.68   $160.70   $160.70  
  Purchase #5 $128.98   3.472%   $133.4582   $133.46   $133.45   $133.50  
  Purchase #6 $176.77   10.690%   $195.6667   $195.67   $195.65   $195.70  
  Purchase #7 $63.46   4.840%   $66.5315   $66.53   $66.55   $66.50  
  7 purchase totals = $1,153.36       $1,256.2314   $1,256.24   $1,256.25   $1,256.30