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 $133.48   8.659%   $145.038   $145.04   $145.05   $145.00  
  Purchase #2 $212.44   10.549%   $234.8503   $234.85   $234.85   $234.90  
  Purchase #3 $184.35   10.515%   $203.7344   $203.73   $203.75   $203.70  
  Purchase #4 $153.41   3.582%   $158.9051   $158.91   $158.90   $158.90  
  Purchase #5 $108.89   12.311%   $122.2954   $122.30   $122.30   $122.30  
  Purchase #6 $156.91   4.431%   $163.8627   $163.86   $163.85   $163.90  
  Purchase #7 $71.97   4.205%   $74.9963   $75.00   $75.00   $75.00  
  7 purchase totals = $1,021.45       $1,103.6822   $1,103.69   $1,103.70   $1,103.70