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	$219.51	12.209%	$246.31	$246.31	$246.30	$246.30
Purchase #2	$105.70	10.249%	$116.5332	$116.53	$116.55	$116.50
Purchase #3	$166.69	8.225%	$180.4003	$180.40	$180.40	$180.40
Purchase #4	$17.31	7.837%	$18.6666	$18.67	$18.65	$18.70
Purchase #5	$168.42	3.525%	$174.3568	$174.36	$174.35	$174.40
Purchase #6	$101.37	10.128%	$111.6368	$111.64	$111.65	$111.60
Purchase #7	$145.69	7.425%	$156.5075	$156.51	$156.50	$156.50
7 purchase totals =	$924.69		$1,004.4112	$1,004.42	$1,004.40	$1,004.40