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 $236.98   13.279%   $268.4486   $268.45   $268.45   $268.40  
  Purchase #2 $212.44   8.199%   $229.858   $229.86   $229.85   $229.90  
  Purchase #3 $46.96   11.344%   $52.2871   $52.29   $52.30   $52.30  
  Purchase #4 $231.43   4.432%   $241.687   $241.69   $241.70   $241.70  
  Purchase #5 $174.86   10.183%   $192.666   $192.67   $192.65   $192.70  
  Purchase #6 $86.51   13.259%   $97.9804   $97.98   $98.00   $98.00  
  Purchase #7 $52.36   8.703%   $56.9169   $56.92   $56.90   $56.90  
  7 purchase totals = $1,041.54       $1,139.8440   $1,139.86   $1,139.85   $1,139.90