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 $5.72   3.144%   $5.8998   $5.90   $5.90   $5.90  
  Purchase #2 $176.84   12.802%   $199.4791   $199.48   $199.50   $199.50  
  Purchase #3 $8.42   6.721%   $8.9859   $8.99   $9.00   $9.00  
  Purchase #4 $166.41   4.605%   $174.0732   $174.07   $174.05   $174.10  
  Purchase #5 $28.80   9.214%   $31.4536   $31.45   $31.45   $31.50  
  Purchase #6 $215.63   7.869%   $232.5979   $232.60   $232.60   $232.60  
  Purchase #7 $80.73   11.341%   $89.8856   $89.89   $89.90   $89.90  
  7 purchase totals = $682.55       $742.3751   $742.38   $742.40   $742.50