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	$240.46	10.161%	$264.8931	$264.89	$264.90	$264.90
Purchase #2	$233.52	12.721%	$263.2261	$263.23	$263.25	$263.20
Purchase #3	$174.66	6.209%	$185.5046	$185.50	$185.50	$185.50
Purchase #4	$55.72	12.169%	$62.5006	$62.50	$62.50	$62.50
Purchase #5	$27.70	4.226%	$28.8706	$28.87	$28.85	$28.90
Purchase #6	$54.92	9.766%	$60.2835	$60.28	$60.30	$60.30
Purchase #7	$79.67	5.871%	$84.3474	$84.35	$84.35	$84.30
7 purchase totals =	$866.65		$949.6259	$949.62	$949.65	$949.60