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 $88.79   6.259%   $94.3474   $94.35   $94.35   $94.30  
  Purchase #2 $56.77   12.184%   $63.6869   $63.69   $63.70   $63.70  
  Purchase #3 $233.29   3.439%   $241.3128   $241.31   $241.30   $241.30  
  Purchase #4 $99.65   7.773%   $107.3958   $107.40   $107.40   $107.40  
  Purchase #5 $192.98   10.654%   $213.5401   $213.54   $213.55   $213.50  
  Purchase #6 $176.58   12.176%   $198.0804   $198.08   $198.10   $198.10  
  Purchase #7 $239.42   4.824%   $250.9696   $250.97   $250.95   $251.00  
  7 purchase totals = $1,087.48       $1,169.3330   $1,169.34   $1,169.35   $1,169.30