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	$15.55	5.177%	$16.355	$16.36	$16.35	$16.40
Purchase #2	$104.85	5.488%	$110.6042	$110.60	$110.60	$110.60
Purchase #3	$140.33	12.787%	$158.274	$158.27	$158.25	$158.30
Purchase #4	$137.85	6.548%	$146.8764	$146.88	$146.90	$146.90
Purchase #5	$183.88	6.764%	$196.3176	$196.32	$196.30	$196.30
Purchase #6	$239.42	7.394%	$257.1227	$257.12	$257.10	$257.10
Purchase #7	$191.25	12.416%	$214.9956	$215.00	$215.00	$215.00
7 purchase totals =	$1,013.13		$1,100.5455	$1,100.55	$1,100.50	$1,100.60