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	$56.69	4.628%	$59.3136	$59.31	$59.30	$59.30
Purchase #2	$136.77	13.124%	$154.7197	$154.72	$154.70	$154.70
Purchase #3	$111.72	10.278%	$123.2026	$123.20	$123.20	$123.20
Purchase #4	$153.91	5.507%	$162.3858	$162.39	$162.40	$162.40
Purchase #5	$178.64	5.814%	$189.0261	$189.03	$189.05	$189.00
Purchase #6	$76.96	12.636%	$86.6847	$86.68	$86.70	$86.70
Purchase #7	$243.44	8.104%	$263.1684	$263.17	$263.15	$263.20
7 purchase totals =	$958.13		$1,038.5009	$1,038.50	$1,038.50	$1,038.50