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 $22.29   12.757%   $25.1335   $25.13   $25.15   $25.10  
  Purchase #2 $236.96   9.373%   $259.1703   $259.17   $259.15   $259.20  
  Purchase #3 $175.41   9.176%   $191.5056   $191.51   $191.50   $191.50  
  Purchase #4 $244.27   4.163%   $254.439   $254.44   $254.45   $254.40  
  Purchase #5 $84.89   12.690%   $95.6625   $95.66   $95.65   $95.70  
  Purchase #6 $101.66   5.420%   $107.17   $107.17   $107.15   $107.20  
  Purchase #7 $137.53   7.631%   $148.0249   $148.02   $148.00   $148.00  
  7 purchase totals = $1,003.01       $1,081.1058   $1,081.10   $1,081.05   $1,081.10