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 $178.87   10.661%   $197.9393   $197.94   $197.95   $197.90  
  Purchase #2 $109.33   12.476%   $122.97   $122.97   $122.95   $123.00  
  Purchase #3 $131.73   11.870%   $147.3664   $147.37   $147.35   $147.40  
  Purchase #4 $76.28   3.856%   $79.2214   $79.22   $79.20   $79.20  
  Purchase #5 $50.68   7.545%   $54.5038   $54.50   $54.50   $54.50  
  Purchase #6 $77.49   6.159%   $82.2626   $82.26   $82.25   $82.30  
  Purchase #7 $63.65   7.752%   $68.5841   $68.58   $68.60   $68.60  
  7 purchase totals = $688.03       $752.8476   $752.84   $752.80   $752.90