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 $87.26   6.509%   $92.9398   $92.94   $92.95   $92.90  
  Purchase #2 $102.83   3.351%   $106.2758   $106.28   $106.30   $106.30  
  Purchase #3 $81.99   6.718%   $87.4981   $87.50   $87.50   $87.50  
  Purchase #4 $54.71   10.196%   $60.2882   $60.29   $60.30   $60.30  
  Purchase #5 $39.66   4.330%   $41.3773   $41.38   $41.40   $41.40  
  Purchase #6 $205.60   11.863%   $229.9903   $229.99   $230.00   $230.00  
  Purchase #7 $236.63   7.831%   $255.1605   $255.16   $255.15   $255.20  
  7 purchase totals = $808.68       $873.5300   $873.54   $873.60   $873.60