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	$105.48	3.636%	$109.3153	$109.32	$109.30	$109.30
Purchase #2	$128.98	4.112%	$134.2837	$134.28	$134.30	$134.30
Purchase #3	$141.56	6.285%	$150.457	$150.46	$150.45	$150.50
Purchase #4	$10.28	13.552%	$11.6731	$11.67	$11.65	$11.70
Purchase #5	$219.58	4.559%	$229.5907	$229.59	$229.60	$229.60
Purchase #6	$154.86	8.214%	$167.5802	$167.58	$167.60	$167.60
Purchase #7	$39.84	9.736%	$43.7188	$43.72	$43.70	$43.70
7 purchase totals =	$800.58		$846.6188	$846.62	$846.60	$846.70