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	$11.26	11.200%	$12.5211	$12.52	$12.50	$12.50
Purchase #2	$71.39	8.185%	$77.2333	$77.23	$77.25	$77.20
Purchase #3	$40.88	10.624%	$45.2231	$45.22	$45.20	$45.20
Purchase #4	$131.40	13.596%	$149.2651	$149.27	$149.25	$149.30
Purchase #5	$175.93	4.514%	$183.8715	$183.87	$183.85	$183.90
Purchase #6	$32.33	4.649%	$33.833	$33.83	$33.85	$33.80
Purchase #7	$133.38	6.749%	$142.3818	$142.38	$142.40	$142.40
7 purchase totals =	$596.57		$644.3289	$644.32	$644.30	$644.30