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 $53.34   5.377%   $56.2081   $56.21   $56.20   $56.20  
  Purchase #2 $174.57   7.514%   $187.6872   $187.69   $187.70   $187.70  
  Purchase #3 $180.88   7.820%   $195.0248   $195.02   $195.00   $195.00  
  Purchase #4 $245.70   11.636%   $274.2897   $274.29   $274.30   $274.30  
  Purchase #5 $236.91   5.344%   $249.5705   $249.57   $249.55   $249.60  
  Purchase #6 $161.62   5.212%   $170.0436   $170.04   $170.05   $170.00  
  Purchase #7 $116.38   8.857%   $126.6878   $126.69   $126.70   $126.70  
  7 purchase totals = $1,169.40       $1,259.5117   $1,259.51   $1,259.50   $1,259.50