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	$175.33	4.739%	$183.6389	$183.64	$183.65	$183.60
Purchase #2	$43.25	5.760%	$45.7412	$45.74	$45.75	$45.70
Purchase #3	$129.56	7.323%	$139.0477	$139.05	$139.05	$139.00
Purchase #4	$27.98	6.716%	$29.8591	$29.86	$29.85	$29.90
Purchase #5	$62.72	4.112%	$65.299	$65.30	$65.30	$65.30
Purchase #6	$247.72	12.827%	$279.495	$279.50	$279.50	$279.50
Purchase #7	$167.88	10.708%	$185.8566	$185.86	$185.85	$185.90
7 purchase totals =	$854.44		$928.9375	$928.95	$928.95	$928.90