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 $210.42   8.447%   $228.1942   $228.19   $228.20   $228.20  
  Purchase #2 $105.36   13.741%   $119.8375   $119.84   $119.85   $119.80  
  Purchase #3 $168.90   11.776%   $188.7897   $188.79   $188.80   $188.80  
  Purchase #4 $116.92   6.108%   $124.0615   $124.06   $124.05   $124.10  
  Purchase #5 $78.40   10.104%   $86.3215   $86.32   $86.30   $86.30  
  Purchase #6 $230.36   11.444%   $256.7224   $256.72   $256.70   $256.70  
  Purchase #7 $51.30   9.687%   $56.2694   $56.27   $56.25   $56.30  
  7 purchase totals = $961.66       $1,060.1962   $1,060.19   $1,060.15   $1,060.20