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 $21.41   10.841%   $23.7311   $23.73   $23.75   $23.70  
  Purchase #2 $211.89   4.424%   $221.264   $221.26   $221.25   $221.30  
  Purchase #3 $178.44   13.596%   $202.7007   $202.70   $202.70   $202.70  
  Purchase #4 $156.58   7.584%   $168.455   $168.46   $168.45   $168.50  
  Purchase #5 $44.33   4.249%   $46.2136   $46.21   $46.20   $46.20  
  Purchase #6 $200.82   5.794%   $212.4555   $212.46   $212.45   $212.50  
  Purchase #7 $131.44   6.211%   $139.6037   $139.60   $139.60   $139.60  
  7 purchase totals = $944.91       $1,014.4236   $1,014.42   $1,014.40   $1,014.50