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	$82.78	8.573%	$89.8767	$89.88	$89.90	$89.90
Purchase #2	$50.75	12.167%	$56.9248	$56.92	$56.90	$56.90
Purchase #3	$247.37	7.556%	$266.0613	$266.06	$266.05	$266.10
Purchase #4	$153.29	3.476%	$158.6184	$158.62	$158.60	$158.60
Purchase #5	$158.49	7.565%	$170.4798	$170.48	$170.50	$170.50
Purchase #6	$193.71	10.430%	$213.914	$213.91	$213.90	$213.90
Purchase #7	$85.28	8.435%	$92.4734	$92.47	$92.45	$92.50
7 purchase totals =	$971.67		$1,048.3484	$1,048.34	$1,048.30	$1,048.40