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 $246.92   10.601%   $273.096   $273.10   $273.10   $273.10  
  Purchase #2 $116.63   9.442%   $127.6422   $127.64   $127.65   $127.60  
  Purchase #3 $200.52   6.725%   $214.005   $214.01   $214.00   $214.00  
  Purchase #4 $66.48   8.276%   $71.9819   $71.98   $72.00   $72.00  
  Purchase #5 $246.68   7.734%   $265.7582   $265.76   $265.75   $265.80  
  Purchase #6 $159.81   11.712%   $178.5269   $178.53   $178.55   $178.50  
  Purchase #7 $208.74   10.689%   $231.0522   $231.05   $231.05   $231.10  
  7 purchase totals = $1,245.78       $1,362.0624   $1,362.07   $1,362.10   $1,362.10