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 $239.58   6.282%   $254.6304   $254.63   $254.65   $254.60  
  Purchase #2 $185.84   3.836%   $192.9688   $192.97   $192.95   $193.00  
  Purchase #3 $160.44   12.591%   $180.641   $180.64   $180.65   $180.60  
  Purchase #4 $243.45   5.653%   $257.2122   $257.21   $257.20   $257.20  
  Purchase #5 $233.78   5.521%   $246.687   $246.69   $246.70   $246.70  
  Purchase #6 $14.89   5.721%   $15.7419   $15.74   $15.75   $15.70  
  Purchase #7 $24.38   5.417%   $25.7007   $25.70   $25.70   $25.70  
  7 purchase totals = $1,102.36       $1,173.5820   $1,173.58   $1,173.60   $1,173.50