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 $168.86   10.133%   $185.9706   $185.97   $185.95   $186.00  
  Purchase #2 $243.83   11.494%   $271.8558   $271.86   $271.85   $271.90  
  Purchase #3 $86.39   7.854%   $93.1751   $93.18   $93.20   $93.20  
  Purchase #4 $158.81   12.214%   $178.2071   $178.21   $178.20   $178.20  
  Purchase #5 $221.38   5.357%   $233.2393   $233.24   $233.25   $233.20  
  Purchase #6 $12.44   10.838%   $13.7882   $13.79   $13.80   $13.80  
  Purchase #7 $129.85   5.258%   $136.6775   $136.68   $136.70   $136.70  
  7 purchase totals = $1,021.56       $1,112.9136   $1,112.93   $1,112.95   $1,113.00