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 $247.31   11.805%   $276.5049   $276.50   $276.50   $276.50  
  Purchase #2 $134.61   6.302%   $143.0931   $143.09   $143.10   $143.10  
  Purchase #3 $42.36   6.488%   $45.1083   $45.11   $45.10   $45.10  
  Purchase #4 $207.84   7.147%   $222.6943   $222.69   $222.70   $222.70  
  Purchase #5 $224.30   5.808%   $237.3273   $237.33   $237.35   $237.30  
  Purchase #6 $119.78   11.839%   $133.9608   $133.96   $133.95   $134.00  
  Purchase #7 $69.84   5.125%   $73.4193   $73.42   $73.40   $73.40  
  7 purchase totals = $1,046.04       $1,132.1080   $1,132.10   $1,132.10   $1,132.10