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 $69.58   8.674%   $75.6154   $75.62   $75.60   $75.60  
  Purchase #2 $85.61   9.844%   $94.0374   $94.04   $94.05   $94.00  
  Purchase #3 $94.87   3.424%   $98.1183   $98.12   $98.10   $98.10  
  Purchase #4 $210.81   10.843%   $233.6681   $233.67   $233.65   $233.70  
  Purchase #5 $5.63   11.294%   $6.2659   $6.27   $6.25   $6.30  
  Purchase #6 $245.39   8.519%   $266.2948   $266.29   $266.30   $266.30  
  Purchase #7 $126.90   4.564%   $132.6917   $132.69   $132.70   $132.70  
  7 purchase totals = $838.79       $906.6916   $906.70   $906.65   $906.70