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 $54.33   12.498%   $61.1202   $61.12   $61.10   $61.10  
  Purchase #2 $215.75   7.235%   $231.3595   $231.36   $231.35   $231.40  
  Purchase #3 $113.66   7.695%   $122.4061   $122.41   $122.40   $122.40  
  Purchase #4 $178.67   9.488%   $195.6222   $195.62   $195.60   $195.60  
  Purchase #5 $21.83   9.582%   $23.9218   $23.92   $23.90   $23.90  
  Purchase #6 $135.74   9.535%   $148.6828   $148.68   $148.70   $148.70  
  Purchase #7 $211.90   10.195%   $233.5032   $233.50   $233.50   $233.50  
  7 purchase totals = $931.88       $1,016.6158   $1,016.61   $1,016.55   $1,016.60