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 $93.28   3.813%   $96.8368   $96.84   $96.85   $96.80  
  Purchase #2 $217.44   12.301%   $244.1873   $244.19   $244.20   $244.20  
  Purchase #3 $216.54   10.522%   $239.3243   $239.32   $239.30   $239.30  
  Purchase #4 $96.45   12.632%   $108.6336   $108.63   $108.65   $108.60  
  Purchase #5 $247.52   7.244%   $265.4503   $265.45   $265.45   $265.50  
  Purchase #6 $166.52   8.324%   $180.3811   $180.38   $180.40   $180.40  
  Purchase #7 $114.73   8.469%   $124.4465   $124.45   $124.45   $124.40  
  7 purchase totals = $1,152.48       $1,259.2599   $1,259.26   $1,259.30   $1,259.20