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 $189.76   11.453%   $211.4932   $211.49   $211.50   $211.50  
  Purchase #2 $66.63   7.487%   $71.6186   $71.62   $71.60   $71.60  
  Purchase #3 $232.34   7.482%   $249.7237   $249.72   $249.70   $249.70  
  Purchase #4 $146.36   4.311%   $152.6696   $152.67   $152.65   $152.70  
  Purchase #5 $146.28   3.872%   $151.944   $151.94   $151.95   $151.90  
  Purchase #6 $136.75   4.137%   $142.4073   $142.41   $142.40   $142.40  
  Purchase #7 $218.94   7.536%   $235.4393   $235.44   $235.45   $235.40  
  7 purchase totals = $1,137.06       $1,215.2957   $1,215.29   $1,215.25   $1,215.20