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	$11.60	13.302%	$13.143	$13.14	$13.15	$13.10
Purchase #2	$193.92	12.179%	$217.5375	$217.54	$217.55	$217.50
Purchase #3	$110.30	3.874%	$114.573	$114.57	$114.55	$114.60
Purchase #4	$56.73	6.501%	$60.418	$60.42	$60.40	$60.40
Purchase #5	$139.46	12.150%	$156.4044	$156.40	$156.40	$156.40
Purchase #6	$30.67	4.369%	$32.01	$32.01	$32.00	$32.00
Purchase #7	$108.39	7.111%	$116.0976	$116.10	$116.10	$116.10
7 purchase totals =	$651.07		$710.1835	$710.18	$710.15	$710.10