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 $250.89   12.523%   $282.309   $282.31   $282.30   $282.30  
  Purchase #2 $121.36   3.546%   $125.6634   $125.66   $125.65   $125.70  
  Purchase #3 $123.80   6.328%   $131.6341   $131.63   $131.65   $131.60  
  Purchase #4 $200.39   6.424%   $213.2631   $213.26   $213.25   $213.30  
  Purchase #5 $219.39   5.248%   $230.9036   $230.90   $230.90   $230.90  
  Purchase #6 $244.69   5.524%   $258.2067   $258.21   $258.20   $258.20  
  Purchase #7 $133.74   5.255%   $140.768   $140.77   $140.75   $140.80  
  7 purchase totals = $1,294.26       $1,382.7479   $1,382.74   $1,382.70   $1,382.80