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	$247.42	6.855%	$264.3806	$264.38	$264.40	$264.40
Purchase #2	$211.44	5.359%	$222.7711	$222.77	$222.75	$222.80
Purchase #3	$219.46	6.226%	$233.1236	$233.12	$233.10	$233.10
Purchase #4	$82.78	8.387%	$89.7228	$89.72	$89.70	$89.70
Purchase #5	$41.52	4.316%	$43.312	$43.31	$43.30	$43.30
Purchase #6	$126.70	12.810%	$142.9303	$142.93	$142.95	$142.90
Purchase #7	$241.59	8.841%	$262.949	$262.95	$262.95	$262.90
7 purchase totals =	$1,170.91		$1,259.1894	$1,259.18	$1,259.15	$1,259.10