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 $202.36   3.522%   $209.4871   $209.49   $209.50   $209.50  
  Purchase #2 $245.54   8.870%   $267.3194   $267.32   $267.30   $267.30  
  Purchase #3 $230.42   11.833%   $257.6856   $257.69   $257.70   $257.70  
  Purchase #4 $30.60   9.208%   $33.4176   $33.42   $33.40   $33.40  
  Purchase #5 $27.81   9.599%   $30.4795   $30.48   $30.50   $30.50  
  Purchase #6 $33.80   6.303%   $35.9304   $35.93   $35.95   $35.90  
  Purchase #7 $176.26   7.503%   $189.4848   $189.48   $189.50   $189.50  
  7 purchase totals = $946.79       $1,023.8044   $1,023.81   $1,023.85   $1,023.80