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	$239.34	6.784%	$255.5768	$255.58	$255.60	$255.60
Purchase #2	$79.89	13.359%	$90.5625	$90.56	$90.55	$90.60
Purchase #3	$173.92	4.742%	$182.1673	$182.17	$182.15	$182.20
Purchase #4	$52.25	10.499%	$57.7357	$57.74	$57.75	$57.70
Purchase #5	$88.52	7.632%	$95.2758	$95.28	$95.30	$95.30
Purchase #6	$215.34	6.715%	$229.8001	$229.80	$229.80	$229.80
Purchase #7	$11.95	10.329%	$13.1843	$13.18	$13.20	$13.20
7 purchase totals =	$861.21		$924.3025	$924.31	$924.35	$924.40