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 $58.33   5.314%   $61.4297   $61.43   $61.45   $61.40  
  Purchase #2 $233.58   11.792%   $261.1238   $261.12   $261.10   $261.10  
  Purchase #3 $107.62   4.478%   $112.4392   $112.44   $112.45   $112.40  
  Purchase #4 $143.62   6.445%   $152.8763   $152.88   $152.90   $152.90  
  Purchase #5 $28.36   3.141%   $29.2508   $29.25   $29.25   $29.30  
  Purchase #6 $239.84   8.192%   $259.4877   $259.49   $259.50   $259.50  
  Purchase #7 $7.32   9.221%   $7.995   $8.00   $8.00   $8.00  
  7 purchase totals = $818.67       $884.6025   $884.61   $884.65   $884.60