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 $247.58   13.781%   $281.699   $281.70   $281.70   $281.70  
  Purchase #2 $118.28   6.716%   $126.2237   $126.22   $126.20   $126.20  
  Purchase #3 $77.74   7.418%   $83.5068   $83.51   $83.50   $83.50  
  Purchase #4 $231.99   3.689%   $240.5481   $240.55   $240.55   $240.50  
  Purchase #5 $178.46   11.569%   $199.106   $199.11   $199.10   $199.10  
  Purchase #6 $230.29   4.325%   $240.25   $240.25   $240.25   $240.30  
  Purchase #7 $137.44   13.269%   $155.6769   $155.68   $155.70   $155.70  
  7 purchase totals = $1,221.78       $1,327.0105   $1,327.02   $1,327.00   $1,327.00