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 $230.84   7.844%   $248.9471   $248.95   $248.95   $248.90  
  Purchase #2 $105.93   12.115%   $118.7634   $118.76   $118.75   $118.80  
  Purchase #3 $175.36   4.839%   $183.8457   $183.85   $183.85   $183.80  
  Purchase #4 $61.58   5.144%   $64.7477   $64.75   $64.75   $64.70  
  Purchase #5 $224.65   7.487%   $241.4695   $241.47   $241.45   $241.50  
  Purchase #6 $222.75   10.154%   $245.368   $245.37   $245.35   $245.40  
  Purchase #7 $244.86   8.581%   $265.8714   $265.87   $265.85   $265.90  
  7 purchase totals = $1,265.97       $1,369.0128   $1,369.02   $1,368.95   $1,369.00