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	$52.92	9.616%	$58.0088	$58.01	$58.00	$58.00
Purchase #2	$241.61	13.463%	$274.138	$274.14	$274.15	$274.10
Purchase #3	$48.69	3.301%	$50.2973	$50.30	$50.30	$50.30
Purchase #4	$53.58	11.670%	$59.8328	$59.83	$59.85	$59.80
Purchase #5	$233.35	9.574%	$255.6909	$255.69	$255.70	$255.70
Purchase #6	$98.65	10.357%	$108.8672	$108.87	$108.85	$108.90
Purchase #7	$48.68	6.864%	$52.0214	$52.02	$52.00	$52.00
7 purchase totals =	$777.48		$858.8564	$858.86	$858.85	$858.80