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 $228.55   8.640%   $248.2967   $248.30   $248.30   $248.30  
  Purchase #2 $176.90   11.834%   $197.8343   $197.83   $197.85   $197.80  
  Purchase #3 $169.25   12.726%   $190.7888   $190.79   $190.80   $190.80  
  Purchase #4 $61.91   9.193%   $67.6014   $67.60   $67.60   $67.60  
  Purchase #5 $220.32   11.255%   $245.117   $245.12   $245.10   $245.10  
  Purchase #6 $173.46   10.803%   $192.1989   $192.20   $192.20   $192.20  
  Purchase #7 $40.96   13.294%   $46.4052   $46.41   $46.40   $46.40  
  7 purchase totals = $1,071.35       $1,188.2423   $1,188.25   $1,188.25   $1,188.20