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	$42.85	6.287%	$45.544	$45.54	$45.55	$45.50
Purchase #2	$12.72	4.453%	$13.2864	$13.29	$13.30	$13.30
Purchase #3	$59.25	12.472%	$66.6397	$66.64	$66.65	$66.60
Purchase #4	$231.54	3.365%	$239.3313	$239.33	$239.35	$239.30
Purchase #5	$221.87	7.479%	$238.4637	$238.46	$238.45	$238.50
Purchase #6	$215.87	12.188%	$242.1802	$242.18	$242.20	$242.20
Purchase #7	$142.94	3.813%	$148.3903	$148.39	$148.40	$148.40
7 purchase totals =	$927.04		$993.8356	$993.83	$993.90	$993.80