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 $129.55   8.845%   $141.0087   $141.01   $141.00   $141.00  
  Purchase #2 $132.93   9.532%   $145.6009   $145.60   $145.60   $145.60  
  Purchase #3 $71.76   4.849%   $75.2396   $75.24   $75.25   $75.20  
  Purchase #4 $40.67   6.534%   $43.3274   $43.33   $43.35   $43.30  
  Purchase #5 $85.35   10.856%   $94.6156   $94.62   $94.60   $94.60  
  Purchase #6 $5.45   4.453%   $5.6927   $5.69   $5.70   $5.70  
  Purchase #7 $211.63   9.499%   $231.7327   $231.73   $231.75   $231.70  
  7 purchase totals = $677.34       $737.2176   $737.22   $737.25   $737.10