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	$71.28	10.229%	$78.5712	$78.57	$78.55	$78.60
Purchase #2	$102.72	6.790%	$109.6947	$109.69	$109.70	$109.70
Purchase #3	$40.40	8.762%	$43.9398	$43.94	$43.95	$43.90
Purchase #4	$18.52	10.335%	$20.434	$20.43	$20.45	$20.40
Purchase #5	$20.91	6.728%	$22.3168	$22.32	$22.30	$22.30
Purchase #6	$151.71	7.649%	$163.3143	$163.31	$163.30	$163.30
Purchase #7	$235.36	3.844%	$244.4072	$244.41	$244.40	$244.40
7 purchase totals =	$640.90		$682.6780	$682.67	$682.65	$682.60