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 $181.43   6.782%   $193.7346   $193.73   $193.75   $193.70  
  Purchase #2 $225.44   10.194%   $248.4214   $248.42   $248.40   $248.40  
  Purchase #3 $63.65   9.814%   $69.8966   $69.90   $69.90   $69.90  
  Purchase #4 $33.36   9.863%   $36.6503   $36.65   $36.65   $36.70  
  Purchase #5 $134.42   12.631%   $151.3986   $151.40   $151.40   $151.40  
  Purchase #6 $148.69   4.651%   $155.6056   $155.61   $155.60   $155.60  
  Purchase #7 $95.25   6.592%   $101.5289   $101.53   $101.55   $101.50  
  7 purchase totals = $882.24       $957.2360   $957.24   $957.25   $957.20