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 $212.71   6.505%   $226.5468   $226.55   $226.55   $226.50  
  Purchase #2 $117.62   8.353%   $127.4448   $127.44   $127.45   $127.40  
  Purchase #3 $248.80   9.789%   $273.155   $273.16   $273.15   $273.20  
  Purchase #4 $7.69   8.311%   $8.3291   $8.33   $8.35   $8.30  
  Purchase #5 $99.83   11.276%   $111.0868   $111.09   $111.10   $111.10  
  Purchase #6 $132.95   9.456%   $145.5218   $145.52   $145.50   $145.50  
  Purchase #7 $76.34   3.715%   $79.176   $79.18   $79.20   $79.20  
  7 purchase totals = $895.94       $971.2603   $971.27   $971.30   $971.20