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 $236.65   13.844%   $269.4118   $269.41   $269.40   $269.40  
  Purchase #2 $97.69   4.365%   $101.9542   $101.95   $101.95   $102.00  
  Purchase #3 $137.35   13.512%   $155.9087   $155.91   $155.90   $155.90  
  Purchase #4 $243.91   9.745%   $267.679   $267.68   $267.70   $267.70  
  Purchase #5 $223.83   13.471%   $253.9821   $253.98   $254.00   $254.00  
  Purchase #6 $38.57   10.388%   $42.5767   $42.58   $42.60   $42.60  
  Purchase #7 $185.78   10.527%   $205.3371   $205.34   $205.35   $205.30  
  7 purchase totals = $1,163.78       $1,296.8496   $1,296.85   $1,296.90   $1,296.90