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 $215.66   11.104%   $239.6069   $239.61   $239.60   $239.60  
  Purchase #2 $162.37   12.308%   $182.3545   $182.35   $182.35   $182.40  
  Purchase #3 $226.69   6.555%   $241.5495   $241.55   $241.55   $241.50  
  Purchase #4 $68.30   8.106%   $73.8364   $73.84   $73.85   $73.80  
  Purchase #5 $103.30   5.746%   $109.2356   $109.24   $109.25   $109.20  
  Purchase #6 $102.77   10.456%   $113.5156   $113.52   $113.50   $113.50  
  Purchase #7 $108.43   8.236%   $117.3603   $117.36   $117.35   $117.40  
  7 purchase totals = $987.52       $1,077.4588   $1,077.47   $1,077.45   $1,077.40