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 $244.48   6.482%   $260.3272   $260.33   $260.35   $260.30  
  Purchase #2 $115.86   12.409%   $130.2371   $130.24   $130.25   $130.20  
  Purchase #3 $243.50   13.151%   $275.5227   $275.52   $275.50   $275.50  
  Purchase #4 $49.87   6.216%   $52.9699   $52.97   $52.95   $53.00  
  Purchase #5 $214.28   10.523%   $236.8287   $236.83   $236.85   $236.80  
  Purchase #6 $118.37   3.493%   $122.5047   $122.50   $122.50   $122.50  
  Purchase #7 $143.73   3.180%   $148.3006   $148.30   $148.30   $148.30  
  7 purchase totals = $1,130.09       $1,226.6909   $1,226.69   $1,226.70   $1,226.60