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 $232.32   8.684%   $252.4947   $252.49   $252.50   $252.50  
  Purchase #2 $174.68   10.575%   $193.1524   $193.15   $193.15   $193.20  
  Purchase #3 $205.78   9.159%   $224.6274   $224.63   $224.65   $224.60  
  Purchase #4 $214.31   3.520%   $221.8537   $221.85   $221.85   $221.90  
  Purchase #5 $109.82   3.402%   $113.5561   $113.56   $113.55   $113.60  
  Purchase #6 $46.77   5.800%   $49.4827   $49.48   $49.50   $49.50  
  Purchase #7 $120.39   6.465%   $128.1732   $128.17   $128.15   $128.20  
  7 purchase totals = $1,104.07       $1,183.3402   $1,183.33   $1,183.35   $1,183.50