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 $237.28   10.782%   $262.8635   $262.86   $262.85   $262.90  
  Purchase #2 $55.71   4.475%   $58.203   $58.20   $58.20   $58.20  
  Purchase #3 $75.31   3.264%   $77.7681   $77.77   $77.75   $77.80  
  Purchase #4 $54.73   10.677%   $60.5735   $60.57   $60.55   $60.60  
  Purchase #5 $82.89   6.447%   $88.2339   $88.23   $88.25   $88.20  
  Purchase #6 $37.87   5.239%   $39.854   $39.85   $39.85   $39.90  
  Purchase #7 $140.47   4.747%   $147.1381   $147.14   $147.15   $147.10  
  7 purchase totals = $684.26       $734.6341   $734.62   $734.60   $734.70