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 $32.77   11.845%   $36.6516   $36.65   $36.65   $36.70  
  Purchase #2 $221.30   13.401%   $250.9564   $250.96   $250.95   $251.00  
  Purchase #3 $60.26   9.560%   $66.0209   $66.02   $66.00   $66.00  
  Purchase #4 $180.61   13.591%   $205.1567   $205.16   $205.15   $205.20  
  Purchase #5 $93.80   5.388%   $98.8539   $98.85   $98.85   $98.90  
  Purchase #6 $94.46   9.141%   $103.0946   $103.09   $103.10   $103.10  
  Purchase #7 $153.99   13.618%   $174.9604   $174.96   $174.95   $175.00  
  7 purchase totals = $837.19       $935.6945   $935.69   $935.65   $935.90