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 $227.73   6.852%   $243.3341   $243.33   $243.35   $243.30  
  Purchase #2 $38.30   10.167%   $42.194   $42.19   $42.20   $42.20  
  Purchase #3 $163.34   12.195%   $183.2593   $183.26   $183.25   $183.30  
  Purchase #4 $159.62   12.162%   $179.033   $179.03   $179.05   $179.00  
  Purchase #5 $103.46   11.397%   $115.2513   $115.25   $115.25   $115.30  
  Purchase #6 $211.66   13.456%   $240.141   $240.14   $240.15   $240.10  
  Purchase #7 $247.92   7.408%   $266.2859   $266.29   $266.30   $266.30  
  7 purchase totals = $1,152.03       $1,269.4986   $1,269.49   $1,269.55   $1,269.50