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 $59.27   11.828%   $66.2805   $66.28   $66.30   $66.30  
  Purchase #2 $90.36   6.617%   $96.3391   $96.34   $96.35   $96.30  
  Purchase #3 $94.37   4.167%   $98.3024   $98.30   $98.30   $98.30  
  Purchase #4 $177.98   11.519%   $198.4815   $198.48   $198.50   $198.50  
  Purchase #5 $112.27   6.335%   $119.3823   $119.38   $119.40   $119.40  
  Purchase #6 $156.54   12.369%   $175.9024   $175.90   $175.90   $175.90  
  Purchase #7 $150.33   7.412%   $161.4725   $161.47   $161.45   $161.50  
  7 purchase totals = $841.12       $916.1607   $916.15   $916.20   $916.20