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 $245.62   7.463%   $263.9506   $263.95   $263.95   $264.00  
  Purchase #2 $157.81   6.246%   $167.6668   $167.67   $167.65   $167.70  
  Purchase #3 $197.79   13.847%   $225.178   $225.18   $225.20   $225.20  
  Purchase #4 $78.38   7.768%   $84.4686   $84.47   $84.45   $84.50  
  Purchase #5 $70.99   7.776%   $76.5102   $76.51   $76.50   $76.50  
  Purchase #6 $60.34   12.512%   $67.8897   $67.89   $67.90   $67.90  
  Purchase #7 $182.81   8.555%   $198.4494   $198.45   $198.45   $198.40  
  7 purchase totals = $993.74       $1,084.1133   $1,084.12   $1,084.10   $1,084.20