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 $230.44   13.677%   $261.9573   $261.96   $261.95   $262.00  
  Purchase #2 $233.57   11.718%   $260.9397   $260.94   $260.95   $260.90  
  Purchase #3 $162.48   7.603%   $174.8334   $174.83   $174.85   $174.80  
  Purchase #4 $48.42   6.219%   $51.4312   $51.43   $51.45   $51.40  
  Purchase #5 $19.26   11.615%   $21.497   $21.50   $21.50   $21.50  
  Purchase #6 $223.72   7.461%   $240.4117   $240.41   $240.40   $240.40  
  Purchase #7 $234.66   13.264%   $265.7853   $265.79   $265.80   $265.80  
  7 purchase totals = $1,152.55       $1,276.8556   $1,276.86   $1,276.90   $1,276.80