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 $245.64   13.612%   $279.0765   $279.08   $279.10   $279.10  
  Purchase #2 $36.65   11.771%   $40.9641   $40.96   $40.95   $41.00  
  Purchase #3 $170.54   7.297%   $182.9843   $182.98   $183.00   $183.00  
  Purchase #4 $237.74   9.577%   $260.5084   $260.51   $260.50   $260.50  
  Purchase #5 $42.51   10.370%   $46.9183   $46.92   $46.90   $46.90  
  Purchase #6 $199.53   4.545%   $208.5986   $208.60   $208.60   $208.60  
  Purchase #7 $22.36   8.546%   $24.2709   $24.27   $24.25   $24.30  
  7 purchase totals = $954.97       $1,043.3211   $1,043.32   $1,043.30   $1,043.40