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	$51.40	5.598%	$54.2774	$54.28	$54.30	$54.30
Purchase #2	$211.91	7.696%	$228.2186	$228.22	$228.20	$228.20
Purchase #3	$207.44	7.192%	$222.3591	$222.36	$222.35	$222.40
Purchase #4	$180.74	6.705%	$192.8586	$192.86	$192.85	$192.90
Purchase #5	$193.85	10.869%	$214.9196	$214.92	$214.90	$214.90
Purchase #6	$180.79	8.734%	$196.5802	$196.58	$196.60	$196.60
Purchase #7	$223.39	4.438%	$233.304	$233.30	$233.30	$233.30
7 purchase totals =	$1,249.52		$1,342.5175	$1,342.52	$1,342.50	$1,342.60