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 $167.27   11.812%   $187.0279   $187.03   $187.05   $187.00  
  Purchase #2 $21.27   4.598%   $22.248   $22.25   $22.25   $22.20  
  Purchase #3 $5.92   11.292%   $6.5885   $6.59   $6.60   $6.60  
  Purchase #4 $182.40   7.818%   $196.66   $196.66   $196.65   $196.70  
  Purchase #5 $211.90   6.756%   $226.216   $226.22   $226.20   $226.20  
  Purchase #6 $192.30   8.529%   $208.7013   $208.70   $208.70   $208.70  
  Purchase #7 $124.74   5.629%   $131.7616   $131.76   $131.75   $131.80  
  7 purchase totals = $905.80       $979.2033   $979.21   $979.20   $979.20