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	$96.99	8.612%	$105.3428	$105.34	$105.35	$105.30
Purchase #2	$38.98	8.138%	$42.1522	$42.15	$42.15	$42.20
Purchase #3	$89.54	3.637%	$92.7966	$92.80	$92.80	$92.80
Purchase #4	$39.75	6.583%	$42.3667	$42.37	$42.35	$42.40
Purchase #5	$19.82	3.791%	$20.5714	$20.57	$20.55	$20.60
Purchase #6	$127.48	4.819%	$133.6233	$133.62	$133.60	$133.60
Purchase #7	$161.50	13.617%	$183.4915	$183.49	$183.50	$183.50
7 purchase totals =	$574.06		$620.3445	$620.34	$620.30	$620.40