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 $227.61   13.213%   $257.6841   $257.68   $257.70   $257.70  
  Purchase #2 $159.76   8.178%   $172.8252   $172.83   $172.85   $172.80  
  Purchase #3 $77.33   11.491%   $86.216   $86.22   $86.20   $86.20  
  Purchase #4 $248.27   10.773%   $275.0161   $275.02   $275.00   $275.00  
  Purchase #5 $206.98   5.467%   $218.2956   $218.30   $218.30   $218.30  
  Purchase #6 $226.62   6.573%   $241.5157   $241.52   $241.50   $241.50  
  Purchase #7 $247.44   8.257%   $267.8711   $267.87   $267.85   $267.90  
  7 purchase totals = $1,394.01       $1,519.4238   $1,519.44   $1,519.40   $1,519.40