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	$43.25	13.529%	$49.1013	$49.10	$49.10	$49.10
Purchase #2	$127.83	12.408%	$143.6911	$143.69	$143.70	$143.70
Purchase #3	$16.29	12.240%	$18.2839	$18.28	$18.30	$18.30
Purchase #4	$124.89	13.180%	$141.3505	$141.35	$141.35	$141.40
Purchase #5	$55.56	7.524%	$59.7403	$59.74	$59.75	$59.70
Purchase #6	$116.41	11.172%	$129.4153	$129.42	$129.40	$129.40
Purchase #7	$41.47	8.233%	$44.8842	$44.88	$44.90	$44.90
7 purchase totals =	$525.70		$586.4666	$586.46	$586.50	$586.50