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 $152.95   10.170%   $168.505   $168.51   $168.50   $168.50  
  Purchase #2 $244.45   8.734%   $265.8003   $265.80   $265.80   $265.80  
  Purchase #3 $127.45   5.628%   $134.6229   $134.62   $134.60   $134.60  
  Purchase #4 $179.35   11.234%   $199.4982   $199.50   $199.50   $199.50  
  Purchase #5 $204.42   4.223%   $213.0527   $213.05   $213.05   $213.10  
  Purchase #6 $211.63   4.378%   $220.8952   $220.90   $220.90   $220.90  
  Purchase #7 $62.59   8.586%   $67.964   $67.96   $67.95   $68.00  
  7 purchase totals = $1,182.84       $1,270.3383   $1,270.34   $1,270.30   $1,270.40