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 $203.60   11.505%   $227.0242   $227.02   $227.00   $227.00  
  Purchase #2 $32.39   9.743%   $35.5458   $35.55   $35.55   $35.50  
  Purchase #3 $57.59   7.174%   $61.7215   $61.72   $61.70   $61.70  
  Purchase #4 $18.70   3.246%   $19.307   $19.31   $19.30   $19.30  
  Purchase #5 $194.36   4.293%   $202.7039   $202.70   $202.70   $202.70  
  Purchase #6 $66.69   5.537%   $70.3826   $70.38   $70.40   $70.40  
  Purchase #7 $119.61   6.201%   $127.027   $127.03   $127.05   $127.00  
  7 purchase totals = $692.94       $743.7120   $743.71   $743.70   $743.60