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 $198.51   13.144%   $224.6022   $224.60   $224.60   $224.60  
  Purchase #2 $89.25   7.291%   $95.7572   $95.76   $95.75   $95.80  
  Purchase #3 $225.55   3.854%   $234.2427   $234.24   $234.25   $234.20  
  Purchase #4 $101.26   5.718%   $107.05   $107.05   $107.05   $107.10  
  Purchase #5 $9.97   3.641%   $10.333   $10.33   $10.35   $10.30  
  Purchase #6 $101.44   6.601%   $108.1361   $108.14   $108.15   $108.10  
  Purchase #7 $229.38   3.399%   $237.1766   $237.18   $237.20   $237.20  
  7 purchase totals = $955.36       $1,017.2978   $1,017.30   $1,017.35   $1,017.30