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 $174.49   4.323%   $182.0332   $182.03   $182.05   $182.00  
  Purchase #2 $214.37   10.554%   $236.9946   $236.99   $237.00   $237.00  
  Purchase #3 $5.90   3.238%   $6.091   $6.09   $6.10   $6.10  
  Purchase #4 $96.58   4.752%   $101.1695   $101.17   $101.15   $101.20  
  Purchase #5 $189.63   11.166%   $210.8041   $210.80   $210.80   $210.80  
  Purchase #6 $168.28   13.256%   $190.5872   $190.59   $190.60   $190.60  
  Purchase #7 $71.36   11.630%   $79.6592   $79.66   $79.65   $79.70  
  7 purchase totals = $920.61       $1,007.3388   $1,007.33   $1,007.35   $1,007.40