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 $228.73   5.698%   $241.763   $241.76   $241.75   $241.80  
  Purchase #2 $47.30   13.538%   $53.7035   $53.70   $53.70   $53.70  
  Purchase #3 $162.53   9.516%   $177.9964   $178.00   $178.00   $178.00  
  Purchase #4 $174.54   3.701%   $180.9997   $181.00   $181.00   $181.00  
  Purchase #5 $174.81   7.537%   $187.9854   $187.99   $188.00   $188.00  
  Purchase #6 $161.61   6.177%   $171.5926   $171.59   $171.60   $171.60  
  Purchase #7 $167.30   4.260%   $174.427   $174.43   $174.45   $174.40  
  7 purchase totals = $1,116.82       $1,188.4676   $1,188.47   $1,188.50   $1,188.50