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 $94.98   10.607%   $105.0545   $105.05   $105.05   $105.10  
  Purchase #2 $164.29   11.242%   $182.7595   $182.76   $182.75   $182.80  
  Purchase #3 $104.30   5.261%   $109.7872   $109.79   $109.80   $109.80  
  Purchase #4 $76.34   9.490%   $83.5847   $83.58   $83.60   $83.60  
  Purchase #5 $137.66   8.599%   $149.4974   $149.50   $149.50   $149.50  
  Purchase #6 $115.94   3.240%   $119.6965   $119.70   $119.70   $119.70  
  Purchase #7 $81.91   13.156%   $92.6861   $92.69   $92.70   $92.70  
  7 purchase totals = $775.42       $843.0659   $843.07   $843.10   $843.20