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 $245.75   5.852%   $260.1313   $260.13   $260.15   $260.10  
  Purchase #2 $233.88   5.663%   $247.1246   $247.12   $247.10   $247.10  
  Purchase #3 $6.51   7.338%   $6.9877   $6.99   $7.00   $7.00  
  Purchase #4 $73.98   5.824%   $78.2886   $78.29   $78.30   $78.30  
  Purchase #5 $232.79   13.261%   $263.6603   $263.66   $263.65   $263.70  
  Purchase #6 $151.53   3.162%   $156.3214   $156.32   $156.30   $156.30  
  Purchase #7 $11.88   8.738%   $12.9181   $12.92   $12.90   $12.90  
  7 purchase totals = $956.32       $1,025.4320   $1,025.43   $1,025.40   $1,025.40