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 $59.89   5.113%   $62.9522   $62.95   $62.95   $63.00  
  Purchase #2 $165.60   8.793%   $180.1612   $180.16   $180.15   $180.20  
  Purchase #3 $184.76   7.857%   $199.2766   $199.28   $199.30   $199.30  
  Purchase #4 $240.53   3.164%   $248.1404   $248.14   $248.15   $248.10  
  Purchase #5 $76.59   6.429%   $81.514   $81.51   $81.50   $81.50  
  Purchase #6 $53.46   12.821%   $60.3141   $60.31   $60.30   $60.30  
  Purchase #7 $129.38   3.401%   $133.7802   $133.78   $133.80   $133.80  
  7 purchase totals = $910.21       $966.1387   $966.13   $966.15   $966.20