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 $67.68   9.196%   $73.9039   $73.90   $73.90   $73.90  
  Purchase #2 $215.73   9.827%   $236.9298   $236.93   $236.95   $236.90  
  Purchase #3 $193.66   5.204%   $203.7381   $203.74   $203.75   $203.70  
  Purchase #4 $18.25   3.701%   $18.9254   $18.93   $18.95   $18.90  
  Purchase #5 $69.36   5.439%   $73.1325   $73.13   $73.15   $73.10  
  Purchase #6 $19.49   7.710%   $20.9927   $20.99   $21.00   $21.00  
  Purchase #7 $235.56   5.537%   $248.603   $248.60   $248.60   $248.60  
  7 purchase totals = $819.73       $876.2254   $876.22   $876.30   $876.10