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 $88.97   10.310%   $98.1428   $98.14   $98.15   $98.10  
  Purchase #2 $157.30   12.246%   $176.563   $176.56   $176.55   $176.60  
  Purchase #3 $212.75   13.133%   $240.6905   $240.69   $240.70   $240.70  
  Purchase #4 $247.61   4.188%   $257.9799   $257.98   $258.00   $258.00  
  Purchase #5 $82.57   5.188%   $86.8537   $86.85   $86.85   $86.90  
  Purchase #6 $155.33   4.474%   $162.2795   $162.28   $162.30   $162.30  
  Purchase #7 $105.97   6.699%   $113.0689   $113.07   $113.05   $113.10  
  7 purchase totals = $1,050.50       $1,135.5783   $1,135.57   $1,135.60   $1,135.70