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 $234.39   6.504%   $249.6347   $249.63   $249.65   $249.60  
  Purchase #2 $23.72   10.391%   $26.1847   $26.18   $26.20   $26.20  
  Purchase #3 $199.47   13.695%   $226.7874   $226.79   $226.80   $226.80  
  Purchase #4 $58.36   8.493%   $63.3165   $63.32   $63.30   $63.30  
  Purchase #5 $156.94   12.337%   $176.3017   $176.30   $176.30   $176.30  
  Purchase #6 $203.95   8.756%   $221.8079   $221.81   $221.80   $221.80  
  Purchase #7 $134.31   4.426%   $140.2546   $140.25   $140.25   $140.30  
  7 purchase totals = $1,011.14       $1,104.2875   $1,104.28   $1,104.30   $1,104.30