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 $195.61   11.621%   $218.3418   $218.34   $218.35   $218.30  
  Purchase #2 $113.49   5.393%   $119.6105   $119.61   $119.60   $119.60  
  Purchase #3 $26.87   6.467%   $28.6077   $28.61   $28.60   $28.60  
  Purchase #4 $152.41   12.117%   $170.8775   $170.88   $170.90   $170.90  
  Purchase #5 $114.26   9.464%   $125.0736   $125.07   $125.05   $125.10  
  Purchase #6 $85.47   11.104%   $94.9606   $94.96   $94.95   $95.00  
  Purchase #7 $240.34   10.761%   $266.203   $266.20   $266.20   $266.20  
  7 purchase totals = $928.45       $1,023.6747   $1,023.67   $1,023.65   $1,023.70