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	$110.70	11.234%	$123.136	$123.14	$123.15	$123.10
Purchase #2	$28.87	8.620%	$31.3586	$31.36	$31.35	$31.40
Purchase #3	$74.69	8.637%	$81.141	$81.14	$81.15	$81.10
Purchase #4	$14.39	4.612%	$15.0537	$15.05	$15.05	$15.10
Purchase #5	$226.75	10.304%	$250.1143	$250.11	$250.10	$250.10
Purchase #6	$56.35	6.241%	$59.8668	$59.87	$59.85	$59.90
Purchase #7	$72.82	8.106%	$78.7228	$78.72	$78.70	$78.70
7 purchase totals =	$584.57		$639.3932	$639.39	$639.35	$639.40