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 $36.80   5.503%   $38.8251   $38.83   $38.85   $38.80  
  Purchase #2 $25.83   8.200%   $27.9481   $27.95   $27.95   $27.90  
  Purchase #3 $77.29   13.125%   $87.4343   $87.43   $87.45   $87.40  
  Purchase #4 $154.85   8.660%   $168.26   $168.26   $168.25   $168.30  
  Purchase #5 $207.63   8.708%   $225.7104   $225.71   $225.70   $225.70  
  Purchase #6 $12.34   11.615%   $13.7733   $13.77   $13.75   $13.80  
  Purchase #7 $79.99   13.318%   $90.6431   $90.64   $90.65   $90.60  
  7 purchase totals = $594.73       $652.5943   $652.59   $652.60   $652.50