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 $151.76   9.636%   $166.3836   $166.38   $166.40   $166.40  
  Purchase #2 $32.80   12.511%   $36.9036   $36.90   $36.90   $36.90  
  Purchase #3 $155.72   9.669%   $170.7766   $170.78   $170.80   $170.80  
  Purchase #4 $48.98   7.794%   $52.7975   $52.80   $52.80   $52.80  
  Purchase #5 $215.61   11.124%   $239.5945   $239.59   $239.60   $239.60  
  Purchase #6 $248.77   11.646%   $277.7418   $277.74   $277.75   $277.70  
  Purchase #7 $142.27   12.792%   $160.4692   $160.47   $160.45   $160.50  
  7 purchase totals = $995.91       $1,104.6668   $1,104.66   $1,104.70   $1,104.70