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 $223.83   13.541%   $254.1388   $254.14   $254.15   $254.10  
  Purchase #2 $103.84   12.287%   $116.5988   $116.60   $116.60   $116.60  
  Purchase #3 $237.59   5.110%   $249.7308   $249.73   $249.75   $249.70  
  Purchase #4 $158.26   12.812%   $178.5363   $178.54   $178.55   $178.50  
  Purchase #5 $180.46   4.325%   $188.2649   $188.26   $188.25   $188.30  
  Purchase #6 $79.49   9.699%   $87.1997   $87.20   $87.20   $87.20  
  Purchase #7 $166.67   5.433%   $175.7252   $175.73   $175.75   $175.70  
  7 purchase totals = $1,150.14       $1,250.1945   $1,250.20   $1,250.25   $1,250.10