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	$5.84	12.503%	$6.5702	$6.57	$6.55	$6.60
Purchase #2	$197.41	12.108%	$221.3124	$221.31	$221.30	$221.30
Purchase #3	$154.55	12.496%	$173.8626	$173.86	$173.85	$173.90
Purchase #4	$183.52	7.857%	$197.9392	$197.94	$197.95	$197.90
Purchase #5	$185.45	6.178%	$196.9071	$196.91	$196.90	$196.90
Purchase #6	$18.94	5.804%	$20.0393	$20.04	$20.05	$20.00
Purchase #7	$62.60	13.639%	$71.138	$71.14	$71.15	$71.10
7 purchase totals =	$808.31		$887.7688	$887.77	$887.75	$887.70