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	$84.79	5.315%	$89.2966	$89.30	$89.30	$89.30
Purchase #2	$113.64	12.216%	$127.5223	$127.52	$127.50	$127.50
Purchase #3	$178.54	10.156%	$196.6725	$196.67	$196.65	$196.70
Purchase #4	$11.72	12.206%	$13.1505	$13.15	$13.15	$13.20
Purchase #5	$189.41	10.530%	$209.3549	$209.35	$209.35	$209.40
Purchase #6	$60.51	8.593%	$65.7096	$65.71	$65.70	$65.70
Purchase #7	$144.66	6.132%	$153.5306	$153.53	$153.55	$153.50
7 purchase totals =	$783.27		$855.2370	$855.23	$855.20	$855.30