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 $26.53   9.577%   $29.0708   $29.07   $29.05   $29.10  
  Purchase #2 $127.82   9.559%   $140.0383   $140.04   $140.05   $140.00  
  Purchase #3 $243.88   11.122%   $271.0043   $271.00   $271.00   $271.00  
  Purchase #4 $243.35   4.217%   $253.6121   $253.61   $253.60   $253.60  
  Purchase #5 $97.80   11.333%   $108.8837   $108.88   $108.90   $108.90  
  Purchase #6 $185.97   7.495%   $199.9085   $199.91   $199.90   $199.90  
  Purchase #7 $127.48   12.510%   $143.4277   $143.43   $143.45   $143.40  
  7 purchase totals = $1,052.83       $1,145.9454   $1,145.94   $1,145.95   $1,145.90