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 $221.58   12.572%   $249.437   $249.44   $249.45   $249.40  
  Purchase #2 $224.49   8.696%   $244.0117   $244.01   $244.00   $244.00  
  Purchase #3 $43.33   3.522%   $44.8561   $44.86   $44.85   $44.90  
  Purchase #4 $101.73   4.631%   $106.4411   $106.44   $106.45   $106.40  
  Purchase #5 $49.88   12.642%   $56.1858   $56.19   $56.20   $56.20  
  Purchase #6 $240.59   10.682%   $266.2898   $266.29   $266.30   $266.30  
  Purchase #7 $43.54   7.614%   $46.8551   $46.86   $46.85   $46.90  
  7 purchase totals = $925.14       $1,014.0766   $1,014.09   $1,014.10   $1,014.10