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 $57.72   13.809%   $65.6906   $65.69   $65.70   $65.70  
  Purchase #2 $245.86   5.249%   $258.7652   $258.77   $258.75   $258.80  
  Purchase #3 $70.42   3.287%   $72.7347   $72.73   $72.75   $72.70  
  Purchase #4 $167.76   9.400%   $183.5294   $183.53   $183.55   $183.50  
  Purchase #5 $249.92   10.482%   $276.1166   $276.12   $276.10   $276.10  
  Purchase #6 $163.83   12.439%   $184.2088   $184.21   $184.20   $184.20  
  Purchase #7 $126.73   11.401%   $141.1785   $141.18   $141.20   $141.20  
  7 purchase totals = $1,082.24       $1,182.2238   $1,182.23   $1,182.25   $1,182.20