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 $90.49   8.771%   $98.4269   $98.43   $98.45   $98.40  
  Purchase #2 $136.30   13.380%   $154.5369   $154.54   $154.55   $154.50  
  Purchase #3 $88.52   11.396%   $98.6077   $98.61   $98.60   $98.60  
  Purchase #4 $76.39   6.388%   $81.2698   $81.27   $81.25   $81.30  
  Purchase #5 $224.45   6.564%   $239.1829   $239.18   $239.20   $239.20  
  Purchase #6 $169.61   9.516%   $185.7501   $185.75   $185.75   $185.80  
  Purchase #7 $195.37   12.388%   $219.5724   $219.57   $219.55   $219.60  
  7 purchase totals = $981.13       $1,077.3467   $1,077.35   $1,077.35   $1,077.40