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 $26.98   8.384%   $29.242   $29.24   $29.25   $29.20  
  Purchase #2 $23.39   5.185%   $24.6028   $24.60   $24.60   $24.60  
  Purchase #3 $174.34   10.826%   $193.214   $193.21   $193.20   $193.20  
  Purchase #4 $105.28   12.339%   $118.2705   $118.27   $118.25   $118.30  
  Purchase #5 $96.62   8.670%   $104.997   $105.00   $105.00   $105.00  
  Purchase #6 $238.83   9.275%   $260.9815   $260.98   $261.00   $261.00  
  Purchase #7 $245.59   4.416%   $256.4353   $256.44   $256.45   $256.40  
  7 purchase totals = $911.03       $987.7431   $987.74   $987.75   $987.70