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 $176.63   12.188%   $198.1577   $198.16   $198.15   $198.20  
  Purchase #2 $171.59   8.566%   $186.2884   $186.29   $186.30   $186.30  
  Purchase #3 $136.42   11.574%   $152.2093   $152.21   $152.20   $152.20  
  Purchase #4 $69.62   9.387%   $76.1552   $76.16   $76.15   $76.20  
  Purchase #5 $209.46   4.668%   $219.2376   $219.24   $219.25   $219.20  
  Purchase #6 $68.93   5.413%   $72.6612   $72.66   $72.65   $72.70  
  Purchase #7 $120.41   6.863%   $128.6737   $128.67   $128.65   $128.70  
  7 purchase totals = $953.06       $1,033.3831   $1,033.39   $1,033.35   $1,033.50