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	$8.98	11.106%	$9.9773	$9.98	$10.00	$10.00
Purchase #2	$79.63	4.111%	$82.9036	$82.90	$82.90	$82.90
Purchase #3	$238.81	5.454%	$251.8347	$251.83	$251.85	$251.80
Purchase #4	$215.44	9.279%	$235.4307	$235.43	$235.45	$235.40
Purchase #5	$69.73	3.720%	$72.324	$72.32	$72.30	$72.30
Purchase #6	$74.25	11.424%	$82.7323	$82.73	$82.75	$82.70
Purchase #7	$57.26	7.230%	$61.3999	$61.40	$61.40	$61.40
7 purchase totals =	$744.10		$796.6025	$796.59	$796.65	$796.50