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	$62.63	10.664%	$69.3089	$69.31	$69.30	$69.30
Purchase #2	$36.90	9.709%	$40.4826	$40.48	$40.50	$40.50
Purchase #3	$11.47	4.608%	$11.9985	$12.00	$12.00	$12.00
Purchase #4	$86.94	10.866%	$96.3869	$96.39	$96.40	$96.40
Purchase #5	$82.95	8.762%	$90.2181	$90.22	$90.20	$90.20
Purchase #6	$165.82	10.502%	$183.2344	$183.23	$183.25	$183.20
Purchase #7	$78.54	9.395%	$85.9188	$85.92	$85.90	$85.90
7 purchase totals =	$525.25		$577.5482	$577.55	$577.55	$577.50