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 $154.82   9.133%   $168.9597   $168.96   $168.95   $169.00  
  Purchase #2 $43.59   9.346%   $47.6639   $47.66   $47.65   $47.70  
  Purchase #3 $151.68   6.714%   $161.8638   $161.86   $161.85   $161.90  
  Purchase #4 $241.53   11.861%   $270.1779   $270.18   $270.20   $270.20  
  Purchase #5 $128.81   9.663%   $141.2569   $141.26   $141.25   $141.30  
  Purchase #6 $68.82   13.559%   $78.1513   $78.15   $78.15   $78.20  
  Purchase #7 $92.75   6.478%   $98.7583   $98.76   $98.75   $98.80  
  7 purchase totals = $882.00       $966.8318   $966.83   $966.80   $967.10