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 $239.50   8.543%   $259.9605   $259.96   $259.95   $260.00  
  Purchase #2 $228.62   5.443%   $241.0638   $241.06   $241.05   $241.10  
  Purchase #3 $184.43   5.221%   $194.0591   $194.06   $194.05   $194.10  
  Purchase #4 $242.25   13.700%   $275.4383   $275.44   $275.45   $275.40  
  Purchase #5 $230.51   10.833%   $255.4811   $255.48   $255.50   $255.50  
  Purchase #6 $95.97   12.824%   $108.2772   $108.28   $108.30   $108.30  
  Purchase #7 $158.83   8.528%   $172.375   $172.38   $172.40   $172.40  
  7 purchase totals = $1,380.11       $1,506.6550   $1,506.66   $1,506.70   $1,506.80