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 $61.85   7.582%   $66.5395   $66.54   $66.55   $66.50  
  Purchase #2 $85.67   12.827%   $96.6589   $96.66   $96.65   $96.70  
  Purchase #3 $117.68   10.389%   $129.9058   $129.91   $129.90   $129.90  
  Purchase #4 $233.65   6.143%   $248.0031   $248.00   $248.00   $248.00  
  Purchase #5 $18.49   5.856%   $19.5728   $19.57   $19.55   $19.60  
  Purchase #6 $80.46   5.662%   $85.0156   $85.02   $85.00   $85.00  
  Purchase #7 $184.30   12.505%   $207.3467   $207.35   $207.35   $207.30  
  7 purchase totals = $782.10       $853.0424   $853.05   $853.00   $853.00