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 $241.81   9.161%   $263.9622   $263.96   $263.95   $264.00  
  Purchase #2 $234.66   10.708%   $259.7874   $259.79   $259.80   $259.80  
  Purchase #3 $105.53   10.578%   $116.693   $116.69   $116.70   $116.70  
  Purchase #4 $119.49   4.120%   $124.413   $124.41   $124.40   $124.40  
  Purchase #5 $227.58   8.742%   $247.475   $247.48   $247.50   $247.50  
  Purchase #6 $21.76   12.264%   $24.4286   $24.43   $24.45   $24.40  
  Purchase #7 $44.27   13.755%   $50.3593   $50.36   $50.35   $50.40  
  7 purchase totals = $995.10       $1,087.1185   $1,087.12   $1,087.15   $1,087.20