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 $250.42   7.461%   $269.1038   $269.10   $269.10   $269.10  
  Purchase #2 $158.39   11.559%   $176.6983   $176.70   $176.70   $176.70  
  Purchase #3 $75.39   11.287%   $83.8993   $83.90   $83.90   $83.90  
  Purchase #4 $114.32   12.129%   $128.1859   $128.19   $128.20   $128.20  
  Purchase #5 $195.88   5.364%   $206.387   $206.39   $206.40   $206.40  
  Purchase #6 $12.47   8.828%   $13.5709   $13.57   $13.55   $13.60  
  Purchase #7 $74.36   8.811%   $80.9119   $80.91   $80.90   $80.90  
  7 purchase totals = $881.23       $958.7571   $958.76   $958.75   $958.80