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	$163.99	6.439%	$174.5493	$174.55	$174.55	$174.50
Purchase #2	$127.46	10.791%	$141.2142	$141.21	$141.20	$141.20
Purchase #3	$153.67	9.650%	$168.4992	$168.50	$168.50	$168.50
Purchase #4	$21.47	11.452%	$23.9287	$23.93	$23.95	$23.90
Purchase #5	$72.26	9.205%	$78.9115	$78.91	$78.90	$78.90
Purchase #6	$39.87	4.214%	$41.5501	$41.55	$41.55	$41.60
Purchase #7	$30.89	3.207%	$31.8806	$31.88	$31.90	$31.90
7 purchase totals =	$609.61		$660.5336	$660.53	$660.55	$660.50