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 $55.65   13.582%   $63.2084   $63.21   $63.20   $63.20  
  Purchase #2 $168.26   9.500%   $184.2447   $184.24   $184.25   $184.20  
  Purchase #3 $198.49   3.524%   $205.4848   $205.48   $205.50   $205.50  
  Purchase #4 $239.42   10.252%   $263.9653   $263.97   $263.95   $264.00  
  Purchase #5 $48.54   5.693%   $51.3034   $51.30   $51.30   $51.30  
  Purchase #6 $213.89   9.771%   $234.7892   $234.79   $234.80   $234.80  
  Purchase #7 $10.30   4.394%   $10.7526   $10.75   $10.75   $10.80  
  7 purchase totals = $934.55       $1,013.7484   $1,013.74   $1,013.75   $1,013.80