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 $193.89   6.788%   $207.0513   $207.05   $207.05   $207.10  
  Purchase #2 $96.87   9.189%   $105.7714   $105.77   $105.75   $105.80  
  Purchase #3 $235.26   4.550%   $245.9643   $245.96   $245.95   $246.00  
  Purchase #4 $249.65   7.184%   $267.5849   $267.58   $267.60   $267.60  
  Purchase #5 $125.73   4.146%   $130.9428   $130.94   $130.95   $130.90  
  Purchase #6 $200.92   4.762%   $210.4878   $210.49   $210.50   $210.50  
  Purchase #7 $19.61   13.353%   $22.2285   $22.23   $22.25   $22.20  
  7 purchase totals = $1,121.93       $1,190.0310   $1,190.02   $1,190.05   $1,190.10