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 $130.38   12.763%   $147.0204   $147.02   $147.00   $147.00  
  Purchase #2 $113.86   6.838%   $121.6457   $121.65   $121.65   $121.60  
  Purchase #3 $141.75   9.825%   $155.6769   $155.68   $155.70   $155.70  
  Purchase #4 $163.56   7.781%   $176.2866   $176.29   $176.30   $176.30  
  Purchase #5 $209.54   8.663%   $227.6925   $227.69   $227.70   $227.70  
  Purchase #6 $231.35   10.389%   $255.385   $255.39   $255.40   $255.40  
  Purchase #7 $143.58   13.176%   $162.4981   $162.50   $162.50   $162.50  
  7 purchase totals = $1,134.02       $1,246.2052   $1,246.22   $1,246.25   $1,246.20