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 $10.91   12.305%   $12.2525   $12.25   $12.25   $12.30  
  Purchase #2 $69.33   10.761%   $76.7906   $76.79   $76.80   $76.80  
  Purchase #3 $180.77   8.654%   $196.4138   $196.41   $196.40   $196.40  
  Purchase #4 $242.37   12.526%   $272.7293   $272.73   $272.75   $272.70  
  Purchase #5 $121.27   3.151%   $125.0912   $125.09   $125.10   $125.10  
  Purchase #6 $11.31   6.158%   $12.0065   $12.01   $12.00   $12.00  
  Purchase #7 $65.94   5.760%   $69.7381   $69.74   $69.75   $69.70  
  7 purchase totals = $701.90       $765.0220   $765.02   $765.05   $765.00