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 $188.73   5.761%   $199.6027   $199.60   $199.60   $199.60  
  Purchase #2 $43.95   12.404%   $49.4016   $49.40   $49.40   $49.40  
  Purchase #3 $117.36   5.592%   $123.9228   $123.92   $123.90   $123.90  
  Purchase #4 $178.68   3.813%   $185.4931   $185.49   $185.50   $185.50  
  Purchase #5 $100.41   10.391%   $110.8436   $110.84   $110.85   $110.80  
  Purchase #6 $171.93   12.734%   $193.8236   $193.82   $193.80   $193.80  
  Purchase #7 $30.87   11.399%   $34.3889   $34.39   $34.40   $34.40  
  7 purchase totals = $831.93       $897.4763   $897.46   $897.45   $897.40