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 $239.35   9.864%   $262.9595   $262.96   $262.95   $263.00  
  Purchase #2 $29.56   12.667%   $33.3044   $33.30   $33.30   $33.30  
  Purchase #3 $146.93   8.526%   $159.4573   $159.46   $159.45   $159.50  
  Purchase #4 $130.76   7.341%   $140.3591   $140.36   $140.35   $140.40  
  Purchase #5 $197.58   8.712%   $214.7932   $214.79   $214.80   $214.80  
  Purchase #6 $56.34   13.439%   $63.9115   $63.91   $63.90   $63.90  
  Purchase #7 $172.79   8.414%   $187.3286   $187.33   $187.35   $187.30  
  7 purchase totals = $973.31       $1,062.1136   $1,062.11   $1,062.10   $1,062.20