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 $246.85   11.617%   $275.5266   $275.53   $275.55   $275.50  
  Purchase #2 $213.47   7.448%   $229.3692   $229.37   $229.35   $229.40  
  Purchase #3 $22.53   6.830%   $24.0688   $24.07   $24.05   $24.10  
  Purchase #4 $231.28   10.154%   $254.7642   $254.76   $254.75   $254.80  
  Purchase #5 $140.88   11.260%   $156.7431   $156.74   $156.75   $156.70  
  Purchase #6 $96.54   9.195%   $105.4169   $105.42   $105.40   $105.40  
  Purchase #7 $65.25   12.821%   $73.6157   $73.62   $73.60   $73.60  
  7 purchase totals = $1,016.80       $1,119.5045   $1,119.51   $1,119.45   $1,119.50