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	$73.67	5.281%	$77.5605	$77.56	$77.55	$77.60
Purchase #2	$172.75	12.196%	$193.8186	$193.82	$193.80	$193.80
Purchase #3	$79.48	11.723%	$88.7974	$88.80	$88.80	$88.80
Purchase #4	$92.31	6.318%	$98.1421	$98.14	$98.15	$98.10
Purchase #5	$249.94	9.559%	$273.8318	$273.83	$273.85	$273.80
Purchase #6	$177.32	10.700%	$196.2932	$196.29	$196.30	$196.30
Purchase #7	$230.99	10.429%	$255.0799	$255.08	$255.10	$255.10
7 purchase totals =	$1,076.46		$1,183.5235	$1,183.52	$1,183.55	$1,183.50