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 $34.49   5.202%   $36.2842   $36.28   $36.30   $36.30  
  Purchase #2 $146.32   3.340%   $151.2071   $151.21   $151.20   $151.20  
  Purchase #3 $213.66   13.529%   $242.5661   $242.57   $242.55   $242.60  
  Purchase #4 $16.56   12.512%   $18.632   $18.63   $18.65   $18.60  
  Purchase #5 $139.45   12.599%   $157.0193   $157.02   $157.00   $157.00  
  Purchase #6 $213.30   9.698%   $233.9858   $233.99   $234.00   $234.00  
  Purchase #7 $148.54   4.749%   $155.5942   $155.59   $155.60   $155.60  
  7 purchase totals = $912.32       $995.2887   $995.29   $995.30   $995.30