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 $95.63   13.507%   $108.5467   $108.55   $108.55   $108.50  
  Purchase #2 $135.38   3.228%   $139.7501   $139.75   $139.75   $139.80  
  Purchase #3 $241.90   12.210%   $271.436   $271.44   $271.45   $271.40  
  Purchase #4 $232.49   9.165%   $253.7977   $253.80   $253.80   $253.80  
  Purchase #5 $56.89   7.518%   $61.167   $61.17   $61.15   $61.20  
  Purchase #6 $9.50   4.591%   $9.9361   $9.94   $9.95   $9.90  
  Purchase #7 $219.28   3.339%   $226.6018   $226.60   $226.60   $226.60  
  7 purchase totals = $991.07       $1,071.2354   $1,071.25   $1,071.25   $1,071.20