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 $242.47   4.434%   $253.2211   $253.22   $253.20   $253.20  
  Purchase #2 $177.79   10.205%   $195.9335   $195.93   $195.95   $195.90  
  Purchase #3 $42.72   4.820%   $44.7791   $44.78   $44.80   $44.80  
  Purchase #4 $60.41   11.176%   $67.1614   $67.16   $67.15   $67.20  
  Purchase #5 $138.43   3.578%   $143.383   $143.38   $143.40   $143.40  
  Purchase #6 $236.99   10.735%   $262.4309   $262.43   $262.45   $262.40  
  Purchase #7 $82.66   6.203%   $87.7874   $87.79   $87.80   $87.80  
  7 purchase totals = $981.47       $1,054.6964   $1,054.69   $1,054.75   $1,054.70