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 $67.94   11.727%   $75.9073   $75.91   $75.90   $75.90  
  Purchase #2 $18.59   10.628%   $20.5657   $20.57   $20.55   $20.60  
  Purchase #3 $114.86   13.383%   $130.2317   $130.23   $130.25   $130.20  
  Purchase #4 $221.54   11.187%   $246.3237   $246.32   $246.30   $246.30  
  Purchase #5 $152.46   4.685%   $159.6028   $159.60   $159.60   $159.60  
  Purchase #6 $247.64   11.254%   $275.5094   $275.51   $275.50   $275.50  
  Purchase #7 $237.91   7.337%   $255.3655   $255.37   $255.35   $255.40  
  7 purchase totals = $1,060.94       $1,163.5061   $1,163.51   $1,163.45   $1,163.50