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 $246.26   5.245%   $259.1763   $259.18   $259.20   $259.20  
  Purchase #2 $244.91   4.318%   $255.4852   $255.49   $255.50   $255.50  
  Purchase #3 $236.88   6.580%   $252.4667   $252.47   $252.45   $252.50  
  Purchase #4 $249.95   4.870%   $262.1226   $262.12   $262.10   $262.10  
  Purchase #5 $77.71   11.517%   $86.6599   $86.66   $86.65   $86.70  
  Purchase #6 $180.71   9.159%   $197.2612   $197.26   $197.25   $197.30  
  Purchase #7 $25.66   13.732%   $29.1836   $29.18   $29.20   $29.20  
  7 purchase totals = $1,262.08       $1,342.3555   $1,342.36   $1,342.35   $1,342.50