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 $211.94   11.682%   $236.6988   $236.70   $236.70   $236.70  
  Purchase #2 $144.89   5.115%   $152.3011   $152.30   $152.30   $152.30  
  Purchase #3 $118.70   8.199%   $128.4322   $128.43   $128.45   $128.40  
  Purchase #4 $182.38   6.712%   $194.6213   $194.62   $194.60   $194.60  
  Purchase #5 $207.64   8.579%   $225.4534   $225.45   $225.45   $225.50  
  Purchase #6 $17.86   8.459%   $19.3708   $19.37   $19.35   $19.40  
  Purchase #7 $205.76   8.740%   $223.7434   $223.74   $223.75   $223.70  
  7 purchase totals = $1,089.17       $1,180.6210   $1,180.61   $1,180.60   $1,180.60