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 $211.53   12.419%   $237.7999   $237.80   $237.80   $237.80  
  Purchase #2 $29.95   4.257%   $31.225   $31.23   $31.25   $31.20  
  Purchase #3 $125.78   10.711%   $139.2523   $139.25   $139.25   $139.30  
  Purchase #4 $149.26   3.581%   $154.605   $154.61   $154.60   $154.60  
  Purchase #5 $213.76   6.346%   $227.3252   $227.33   $227.35   $227.30  
  Purchase #6 $150.56   8.197%   $162.9014   $162.90   $162.90   $162.90  
  Purchase #7 $84.96   12.568%   $95.6378   $95.64   $95.65   $95.60  
  7 purchase totals = $965.80       $1,048.7466   $1,048.76   $1,048.80   $1,048.70