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 $240.43   5.472%   $253.5863   $253.59   $253.60   $253.60  
  Purchase #2 $19.30   3.347%   $19.946   $19.95   $19.95   $19.90  
  Purchase #3 $70.74   11.340%   $78.7619   $78.76   $78.75   $78.80  
  Purchase #4 $67.87   11.253%   $75.5074   $75.51   $75.50   $75.50  
  Purchase #5 $212.27   12.748%   $239.3302   $239.33   $239.35   $239.30  
  Purchase #6 $192.57   9.307%   $210.4925   $210.49   $210.50   $210.50  
  Purchase #7 $159.87   6.771%   $170.6948   $170.69   $170.70   $170.70  
  7 purchase totals = $963.05       $1,048.3191   $1,048.32   $1,048.35   $1,048.30