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 $64.57   3.368%   $66.7447   $66.74   $66.75   $66.70  
  Purchase #2 $119.56   5.353%   $125.96   $125.96   $125.95   $126.00  
  Purchase #3 $107.28   9.639%   $117.6207   $117.62   $117.60   $117.60  
  Purchase #4 $185.41   12.501%   $208.5881   $208.59   $208.60   $208.60  
  Purchase #5 $166.57   12.425%   $187.2663   $187.27   $187.25   $187.30  
  Purchase #6 $141.44   13.250%   $160.1808   $160.18   $160.20   $160.20  
  Purchase #7 $13.91   5.428%   $14.665   $14.67   $14.65   $14.70  
  7 purchase totals = $798.74       $881.0256   $881.03   $881.00   $881.10