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 $194.78   6.194%   $206.8447   $206.84   $206.85   $206.80  
  Purchase #2 $228.36   11.355%   $254.2903   $254.29   $254.30   $254.30  
  Purchase #3 $142.29   12.214%   $159.6693   $159.67   $159.65   $159.70  
  Purchase #4 $221.56   9.512%   $242.6348   $242.63   $242.65   $242.60  
  Purchase #5 $19.64   11.114%   $21.8228   $21.82   $21.80   $21.80  
  Purchase #6 $223.99   7.199%   $240.115   $240.12   $240.10   $240.10  
  Purchase #7 $231.92   6.241%   $246.3941   $246.39   $246.40   $246.40  
  7 purchase totals = $1,262.54       $1,371.7710   $1,371.76   $1,371.75   $1,371.70