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 $88.79   4.289%   $92.5982   $92.60   $92.60   $92.60  
  Purchase #2 $227.78   3.453%   $235.6452   $235.65   $235.65   $235.60  
  Purchase #3 $128.95   12.359%   $144.8869   $144.89   $144.90   $144.90  
  Purchase #4 $163.70   11.350%   $182.28   $182.28   $182.30   $182.30  
  Purchase #5 $69.69   12.193%   $78.1873   $78.19   $78.20   $78.20  
  Purchase #6 $72.74   4.786%   $76.2213   $76.22   $76.20   $76.20  
  Purchase #7 $231.61   4.209%   $241.3585   $241.36   $241.35   $241.40  
  7 purchase totals = $983.26       $1,051.1774   $1,051.19   $1,051.20   $1,051.20