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 $89.38   10.594%   $98.8489   $98.85   $98.85   $98.80  
  Purchase #2 $208.84   13.259%   $236.5301   $236.53   $236.55   $236.50  
  Purchase #3 $107.45   9.290%   $117.4321   $117.43   $117.45   $117.40  
  Purchase #4 $24.26   10.379%   $26.7779   $26.78   $26.80   $26.80  
  Purchase #5 $63.59   4.422%   $66.4019   $66.40   $66.40   $66.40  
  Purchase #6 $191.67   9.678%   $210.2198   $210.22   $210.20   $210.20  
  Purchase #7 $244.47   13.156%   $276.6325   $276.63   $276.65   $276.60  
  7 purchase totals = $929.66       $1,032.8432   $1,032.84   $1,032.90   $1,032.70