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	$42.72	5.242%	$44.9594	$44.96	$44.95	$45.00
Purchase #2	$57.47	8.505%	$62.3578	$62.36	$62.35	$62.40
Purchase #3	$138.59	5.425%	$146.1085	$146.11	$146.10	$146.10
Purchase #4	$194.61	11.795%	$217.5642	$217.56	$217.55	$217.60
Purchase #5	$18.29	13.768%	$20.8082	$20.81	$20.80	$20.80
Purchase #6	$98.44	10.705%	$108.978	$108.98	$109.00	$109.00
Purchase #7	$130.82	7.836%	$141.0711	$141.07	$141.05	$141.10
7 purchase totals =	$680.94		$741.8472	$741.85	$741.80	$742.00