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 $214.69   4.105%   $223.503   $223.50   $223.50   $223.50  
  Purchase #2 $161.44   5.125%   $169.7138   $169.71   $169.70   $169.70  
  Purchase #3 $129.63   11.487%   $144.5206   $144.52   $144.50   $144.50  
  Purchase #4 $91.69   10.864%   $101.6512   $101.65   $101.65   $101.70  
  Purchase #5 $60.27   3.194%   $62.195   $62.20   $62.20   $62.20  
  Purchase #6 $52.54   8.678%   $57.0994   $57.10   $57.10   $57.10  
  Purchase #7 $169.88   4.384%   $177.3275   $177.33   $177.35   $177.30  
  7 purchase totals = $880.14       $936.0105   $936.01   $936.00   $936.00