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 $35.58   3.593%   $36.8584   $36.86   $36.85   $36.90  
  Purchase #2 $174.32   13.409%   $197.6946   $197.69   $197.70   $197.70  
  Purchase #3 $158.30   3.610%   $164.0146   $164.01   $164.00   $164.00  
  Purchase #4 $98.81   13.247%   $111.8994   $111.90   $111.90   $111.90  
  Purchase #5 $240.50   9.206%   $262.6404   $262.64   $262.65   $262.60  
  Purchase #6 $65.36   10.281%   $72.0797   $72.08   $72.10   $72.10  
  Purchase #7 $214.68   4.583%   $224.5188   $224.52   $224.50   $224.50  
  7 purchase totals = $987.55       $1,069.7059   $1,069.70   $1,069.70   $1,069.70