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	$107.25	6.589%	$114.3167	$114.32	$114.30	$114.30
Purchase #2	$39.75	8.749%	$43.2277	$43.23	$43.25	$43.20
Purchase #3	$34.70	9.351%	$37.9448	$37.94	$37.95	$37.90
Purchase #4	$146.31	3.116%	$150.869	$150.87	$150.85	$150.90
Purchase #5	$249.69	11.230%	$277.7302	$277.73	$277.75	$277.70
Purchase #6	$51.29	6.370%	$54.5572	$54.56	$54.55	$54.60
Purchase #7	$102.45	6.617%	$109.2291	$109.23	$109.25	$109.20
7 purchase totals =	$731.44		$787.8747	$787.88	$787.90	$787.80