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 $51.74   10.748%   $57.301   $57.30   $57.30   $57.30  
  Purchase #2 $199.49   11.204%   $221.8409   $221.84   $221.85   $221.80  
  Purchase #3 $65.95   9.495%   $72.212   $72.21   $72.20   $72.20  
  Purchase #4 $119.50   11.240%   $132.9318   $132.93   $132.95   $132.90  
  Purchase #5 $148.33   12.186%   $166.4055   $166.41   $166.40   $166.40  
  Purchase #6 $70.88   3.455%   $73.3289   $73.33   $73.35   $73.30  
  Purchase #7 $239.36   7.773%   $257.9655   $257.97   $257.95   $258.00  
  7 purchase totals = $895.25       $981.9856   $981.99   $982.00   $981.90