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 $224.56   5.239%   $236.3247   $236.32   $236.30   $236.30  
  Purchase #2 $247.99   12.168%   $278.1654   $278.17   $278.15   $278.20  
  Purchase #3 $210.99   11.623%   $235.5134   $235.51   $235.50   $235.50  
  Purchase #4 $158.48   12.615%   $178.4723   $178.47   $178.45   $178.50  
  Purchase #5 $113.51   10.503%   $125.432   $125.43   $125.45   $125.40  
  Purchase #6 $246.62   11.315%   $274.5251   $274.53   $274.55   $274.50  
  Purchase #7 $69.83   13.732%   $79.4191   $79.42   $79.40   $79.40  
  7 purchase totals = $1,271.98       $1,407.8520   $1,407.85   $1,407.80   $1,407.80