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 $126.42   6.262%   $134.3364   $134.34   $134.35   $134.30  
  Purchase #2 $210.53   11.709%   $235.181   $235.18   $235.20   $235.20  
  Purchase #3 $90.85   8.664%   $98.7212   $98.72   $98.70   $98.70  
  Purchase #4 $191.66   11.383%   $213.4767   $213.48   $213.50   $213.50  
  Purchase #5 $108.73   3.444%   $112.4747   $112.47   $112.45   $112.50  
  Purchase #6 $155.81   13.405%   $176.6963   $176.70   $176.70   $176.70  
  Purchase #7 $166.45   5.303%   $175.2768   $175.28   $175.30   $175.30  
  7 purchase totals = $1,050.45       $1,146.1631   $1,146.17   $1,146.20   $1,146.20