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	$56.30	5.744%	$59.5339	$59.53	$59.55	$59.50
Purchase #2	$122.27	9.349%	$133.701	$133.70	$133.70	$133.70
Purchase #3	$123.27	5.865%	$130.4998	$130.50	$130.50	$130.50
Purchase #4	$11.79	7.470%	$12.6707	$12.67	$12.65	$12.70
Purchase #5	$63.35	3.649%	$65.6616	$65.66	$65.65	$65.70
Purchase #6	$210.27	13.188%	$238.0004	$238.00	$238.00	$238.00
Purchase #7	$165.35	10.410%	$182.5629	$182.56	$182.55	$182.60
7 purchase totals =	$752.60		$822.6303	$822.62	$822.60	$822.70