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 $205.69   4.778%   $215.5179   $215.52   $215.50   $215.50  
  Purchase #2 $113.57   6.726%   $121.2087   $121.21   $121.20   $121.20  
  Purchase #3 $6.76   4.651%   $7.0744   $7.07   $7.05   $7.10  
  Purchase #4 $187.99   12.212%   $210.9473   $210.95   $210.95   $210.90  
  Purchase #5 $173.90   12.238%   $195.1819   $195.18   $195.20   $195.20  
  Purchase #6 $48.38   5.309%   $50.9485   $50.95   $50.95   $50.90  
  Purchase #7 $239.63   4.522%   $250.4661   $250.47   $250.45   $250.50  
  7 purchase totals = $975.92       $1,051.3448   $1,051.35   $1,051.30   $1,051.30