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	$230.30	5.397%	$242.7293	$242.73	$242.75	$242.70
Purchase #2	$48.74	9.291%	$53.2684	$53.27	$53.25	$53.30
Purchase #3	$44.87	5.633%	$47.3975	$47.40	$47.40	$47.40
Purchase #4	$128.25	9.857%	$140.8916	$140.89	$140.90	$140.90
Purchase #5	$165.90	3.388%	$171.5207	$171.52	$171.50	$171.50
Purchase #6	$97.93	11.772%	$109.4583	$109.46	$109.45	$109.50
Purchase #7	$120.68	5.334%	$127.1171	$127.12	$127.10	$127.10
7 purchase totals =	$836.67		$892.3829	$892.39	$892.35	$892.40