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 $71.86   5.381%   $75.7268   $75.73   $75.75   $75.70  
  Purchase #2 $75.76   13.853%   $86.255   $86.26   $86.25   $86.30  
  Purchase #3 $137.59   5.839%   $145.6239   $145.62   $145.60   $145.60  
  Purchase #4 $37.97   12.538%   $42.7307   $42.73   $42.75   $42.70  
  Purchase #5 $182.90   11.601%   $204.1182   $204.12   $204.10   $204.10  
  Purchase #6 $191.81   3.743%   $198.9894   $198.99   $199.00   $199.00  
  Purchase #7 $234.88   8.712%   $255.3427   $255.34   $255.35   $255.30  
  7 purchase totals = $932.77       $1,008.7867   $1,008.79   $1,008.80   $1,008.70