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	$139.49	13.797%	$158.7354	$158.74	$158.75	$158.70
Purchase #2	$26.86	7.401%	$28.8479	$28.85	$28.85	$28.80
Purchase #3	$237.84	6.592%	$253.5184	$253.52	$253.50	$253.50
Purchase #4	$165.38	8.402%	$179.2752	$179.28	$179.30	$179.30
Purchase #5	$49.66	8.822%	$54.041	$54.04	$54.05	$54.00
Purchase #6	$219.29	8.734%	$238.4428	$238.44	$238.45	$238.40
Purchase #7	$43.48	4.449%	$45.4144	$45.41	$45.40	$45.40
7 purchase totals =	$882.00		$958.2751	$958.28	$958.30	$958.10