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 $114.63   13.130%   $129.6809   $129.68   $129.70   $129.70  
  Purchase #2 $213.75   13.627%   $242.8777   $242.88   $242.90   $242.90  
  Purchase #3 $167.65   5.693%   $177.1943   $177.19   $177.20   $177.20  
  Purchase #4 $179.42   11.164%   $199.4504   $199.45   $199.45   $199.50  
  Purchase #5 $62.29   13.462%   $70.6755   $70.68   $70.70   $70.70  
  Purchase #6 $146.64   3.329%   $151.5216   $151.52   $151.50   $151.50  
  Purchase #7 $189.60   3.654%   $196.528   $196.53   $196.55   $196.50  
  7 purchase totals = $1,073.98       $1,167.9284   $1,167.93   $1,168.00   $1,168.00