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 $162.38   13.342%   $184.0447   $184.04   $184.05   $184.00  
  Purchase #2 $160.42   11.505%   $178.8763   $178.88   $178.90   $178.90  
  Purchase #3 $183.66   9.798%   $201.655   $201.66   $201.65   $201.70  
  Purchase #4 $115.68   10.804%   $128.1781   $128.18   $128.20   $128.20  
  Purchase #5 $218.68   4.540%   $228.6081   $228.61   $228.60   $228.60  
  Purchase #6 $183.54   9.246%   $200.5101   $200.51   $200.50   $200.50  
  Purchase #7 $155.44   13.805%   $176.8985   $176.90   $176.90   $176.90  
  7 purchase totals = $1,179.80       $1,298.7708   $1,298.78   $1,298.80   $1,298.80