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 $244.42   9.475%   $267.5788   $267.58   $267.60   $267.60  
  Purchase #2 $70.41   7.426%   $75.6386   $75.64   $75.65   $75.60  
  Purchase #3 $63.28   4.106%   $65.8783   $65.88   $65.90   $65.90  
  Purchase #4 $103.73   7.782%   $111.8023   $111.80   $111.80   $111.80  
  Purchase #5 $60.75   6.559%   $64.7346   $64.73   $64.75   $64.70  
  Purchase #6 $136.73   12.368%   $153.6408   $153.64   $153.65   $153.60  
  Purchase #7 $104.31   11.828%   $116.6478   $116.65   $116.65   $116.60  
  7 purchase totals = $783.63       $855.9212   $855.92   $856.00   $855.80