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	$48.71	12.720%	$54.9059	$54.91	$54.90	$54.90
Purchase #2	$81.72	10.452%	$90.2614	$90.26	$90.25	$90.30
Purchase #3	$76.34	8.152%	$82.5632	$82.56	$82.55	$82.60
Purchase #4	$202.70	13.604%	$230.2753	$230.28	$230.30	$230.30
Purchase #5	$240.86	9.654%	$264.1126	$264.11	$264.10	$264.10
Purchase #6	$222.94	6.840%	$238.1891	$238.19	$238.20	$238.20
Purchase #7	$159.81	11.639%	$178.4103	$178.41	$178.40	$178.40
7 purchase totals =	$1,033.08		$1,138.7178	$1,138.72	$1,138.70	$1,138.80