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	$39.79	3.786%	$41.2964	$41.30	$41.30	$41.30
Purchase #2	$177.54	5.834%	$187.8977	$187.90	$187.90	$187.90
Purchase #3	$106.32	3.510%	$110.0518	$110.05	$110.05	$110.10
Purchase #4	$96.84	3.595%	$100.3214	$100.32	$100.30	$100.30
Purchase #5	$75.58	4.319%	$78.8443	$78.84	$78.85	$78.80
Purchase #6	$42.68	9.150%	$46.5852	$46.59	$46.60	$46.60
Purchase #7	$116.73	13.445%	$132.4243	$132.42	$132.40	$132.40
7 purchase totals =	$655.48		$697.4211	$697.42	$697.40	$697.40