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 $240.91   11.214%   $267.9256   $267.93   $267.95   $267.90  
  Purchase #2 $22.74   3.118%   $23.449   $23.45   $23.45   $23.40  
  Purchase #3 $31.33   8.467%   $33.9827   $33.98   $34.00   $34.00  
  Purchase #4 $152.61   11.150%   $169.626   $169.63   $169.65   $169.60  
  Purchase #5 $211.70   10.180%   $233.2511   $233.25   $233.25   $233.30  
  Purchase #6 $116.33   5.460%   $122.6816   $122.68   $122.70   $122.70  
  Purchase #7 $214.99   5.871%   $227.6121   $227.61   $227.60   $227.60  
  7 purchase totals = $990.61       $1,078.5281   $1,078.53   $1,078.60   $1,078.50