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 $86.40   11.543%   $96.3732   $96.37   $96.35   $96.40  
  Purchase #2 $248.48   8.525%   $269.6629   $269.66   $269.65   $269.70  
  Purchase #3 $17.35   8.623%   $18.8461   $18.85   $18.85   $18.80  
  Purchase #4 $90.34   4.466%   $94.3746   $94.37   $94.35   $94.40  
  Purchase #5 $127.73   12.143%   $143.2403   $143.24   $143.25   $143.20  
  Purchase #6 $51.34   11.324%   $57.1537   $57.15   $57.15   $57.20  
  Purchase #7 $210.38   12.221%   $236.0905   $236.09   $236.10   $236.10  
  7 purchase totals = $832.02       $915.7413   $915.73   $915.70   $915.80