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 $60.64   10.297%   $66.8841   $66.88   $66.90   $66.90  
  Purchase #2 $70.37   7.109%   $75.3726   $75.37   $75.35   $75.40  
  Purchase #3 $190.81   8.128%   $206.319   $206.32   $206.30   $206.30  
  Purchase #4 $132.54   11.378%   $147.6204   $147.62   $147.60   $147.60  
  Purchase #5 $89.74   3.423%   $92.8118   $92.81   $92.80   $92.80  
  Purchase #6 $196.47   9.212%   $214.5688   $214.57   $214.55   $214.60  
  Purchase #7 $186.56   7.194%   $199.9811   $199.98   $200.00   $200.00  
  7 purchase totals = $927.13       $1,003.5578   $1,003.55   $1,003.50   $1,003.60