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 $113.81   9.234%   $124.3192   $124.32   $124.30   $124.30  
  Purchase #2 $33.28   13.810%   $37.876   $37.88   $37.90   $37.90  
  Purchase #3 $106.86   12.351%   $120.0583   $120.06   $120.05   $120.10  
  Purchase #4 $174.47   7.324%   $187.2482   $187.25   $187.25   $187.20  
  Purchase #5 $185.75   7.367%   $199.4342   $199.43   $199.45   $199.40  
  Purchase #6 $215.46   13.767%   $245.1224   $245.12   $245.10   $245.10  
  Purchase #7 $191.37   7.277%   $205.296   $205.30   $205.30   $205.30  
  7 purchase totals = $1,021.00       $1,119.3543   $1,119.36   $1,119.35   $1,119.30