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 $108.34   4.668%   $113.3973   $113.40   $113.40   $113.40  
  Purchase #2 $51.43   6.159%   $54.5976   $54.60   $54.60   $54.60  
  Purchase #3 $210.84   5.141%   $221.6793   $221.68   $221.70   $221.70  
  Purchase #4 $83.46   4.363%   $87.1014   $87.10   $87.10   $87.10  
  Purchase #5 $17.83   9.866%   $19.5891   $19.59   $19.60   $19.60  
  Purchase #6 $162.95   12.348%   $183.0711   $183.07   $183.05   $183.10  
  Purchase #7 $152.72   13.105%   $172.734   $172.73   $172.75   $172.70  
  7 purchase totals = $787.57       $852.1698   $852.17   $852.20   $852.20