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	$202.90	11.238%	$225.7019	$225.70	$225.70	$225.70
Purchase #2	$90.66	6.562%	$96.6091	$96.61	$96.60	$96.60
Purchase #3	$40.94	6.640%	$43.6584	$43.66	$43.65	$43.70
Purchase #4	$134.89	10.446%	$148.9806	$148.98	$149.00	$149.00
Purchase #5	$55.32	6.493%	$58.9119	$58.91	$58.90	$58.90
Purchase #6	$95.25	5.223%	$100.2249	$100.22	$100.20	$100.20
Purchase #7	$152.44	8.819%	$165.8837	$165.88	$165.90	$165.90
7 purchase totals =	$772.40		$839.9705	$839.96	$839.95	$840.00