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 $101.58   13.544%   $115.338   $115.34   $115.35   $115.30  
  Purchase #2 $233.29   5.431%   $245.96   $245.96   $245.95   $246.00  
  Purchase #3 $231.35   7.563%   $248.847   $248.85   $248.85   $248.80  
  Purchase #4 $5.41   5.826%   $5.7252   $5.73   $5.75   $5.70  
  Purchase #5 $65.62   13.209%   $74.2877   $74.29   $74.30   $74.30  
  Purchase #6 $143.29   3.522%   $148.3367   $148.34   $148.35   $148.30  
  Purchase #7 $20.62   8.614%   $22.3962   $22.40   $22.40   $22.40  
  7 purchase totals = $801.16       $860.8908   $860.91   $860.95   $860.80