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 $163.67   3.282%   $169.0416   $169.04   $169.05   $169.00  
  Purchase #2 $214.41   12.435%   $241.0719   $241.07   $241.05   $241.10  
  Purchase #3 $62.69   3.193%   $64.6917   $64.69   $64.70   $64.70  
  Purchase #4 $161.83   8.482%   $175.5564   $175.56   $175.55   $175.60  
  Purchase #5 $227.32   12.395%   $255.4963   $255.50   $255.50   $255.50  
  Purchase #6 $196.99   10.144%   $216.9727   $216.97   $216.95   $217.00  
  Purchase #7 $53.25   3.675%   $55.2069   $55.21   $55.20   $55.20  
  7 purchase totals = $1,080.16       $1,178.0375   $1,178.04   $1,178.00   $1,178.10