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	$237.62	8.699%	$258.2906	$258.29	$258.30	$258.30
Purchase #2	$38.68	9.423%	$42.3248	$42.32	$42.30	$42.30
Purchase #3	$12.69	4.332%	$13.2397	$13.24	$13.25	$13.20
Purchase #4	$200.84	9.334%	$219.5864	$219.59	$219.60	$219.60
Purchase #5	$54.27	12.465%	$61.0348	$61.03	$61.05	$61.00
Purchase #6	$151.56	13.426%	$171.9084	$171.91	$171.90	$171.90
Purchase #7	$127.61	8.349%	$138.2642	$138.26	$138.25	$138.30
7 purchase totals =	$823.27		$904.6489	$904.64	$904.65	$904.60