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 $247.61   5.846%   $262.0853   $262.09   $262.10   $262.10  
  Purchase #2 $76.75   11.584%   $85.6407   $85.64   $85.65   $85.60  
  Purchase #3 $230.53   6.694%   $245.9617   $245.96   $245.95   $246.00  
  Purchase #4 $204.31   4.306%   $213.1076   $213.11   $213.10   $213.10  
  Purchase #5 $136.43   11.722%   $152.4223   $152.42   $152.40   $152.40  
  Purchase #6 $42.92   4.342%   $44.7836   $44.78   $44.80   $44.80  
  Purchase #7 $240.77   6.590%   $256.6367   $256.64   $256.65   $256.60  
  7 purchase totals = $1,179.32       $1,260.6379   $1,260.64   $1,260.65   $1,260.60