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	$230.77	3.384%	$238.5793	$238.58	$238.60	$238.60
Purchase #2	$247.62	7.262%	$265.6022	$265.60	$265.60	$265.60
Purchase #3	$78.82	8.483%	$85.5063	$85.51	$85.50	$85.50
Purchase #4	$229.91	11.303%	$255.8967	$255.90	$255.90	$255.90
Purchase #5	$136.55	13.118%	$154.4626	$154.46	$154.45	$154.50
Purchase #6	$123.71	4.847%	$129.7062	$129.71	$129.70	$129.70
Purchase #7	$167.62	10.430%	$185.1028	$185.10	$185.10	$185.10
7 purchase totals =	$1,215.00		$1,314.8561	$1,314.86	$1,314.85	$1,314.90