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	$115.84	9.871%	$127.2746	$127.27	$127.25	$127.30
Purchase #2	$105.33	6.613%	$112.2955	$112.30	$112.30	$112.30
Purchase #3	$39.50	3.255%	$40.7857	$40.79	$40.80	$40.80
Purchase #4	$176.82	4.216%	$184.2747	$184.27	$184.25	$184.30
Purchase #5	$80.89	12.634%	$91.1096	$91.11	$91.10	$91.10
Purchase #6	$53.69	3.686%	$55.669	$55.67	$55.65	$55.70
Purchase #7	$208.69	11.316%	$232.3054	$232.31	$232.30	$232.30
7 purchase totals =	$780.76		$843.7145	$843.72	$843.65	$843.80