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 $172.81   4.244%   $180.1441   $180.14   $180.15   $180.10  
  Purchase #2 $107.87   6.736%   $115.1361   $115.14   $115.15   $115.10  
  Purchase #3 $149.88   5.583%   $158.2478   $158.25   $158.25   $158.20  
  Purchase #4 $37.77   6.565%   $40.2496   $40.25   $40.25   $40.20  
  Purchase #5 $171.69   11.808%   $191.9632   $191.96   $191.95   $192.00  
  Purchase #6 $38.75   3.148%   $39.9699   $39.97   $39.95   $40.00  
  Purchase #7 $59.34   7.701%   $63.9098   $63.91   $63.90   $63.90  
  7 purchase totals = $738.11       $789.6205   $789.62   $789.60   $789.50