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	$42.31	9.640%	$46.3887	$46.39	$46.40	$46.40
Purchase #2	$45.89	11.298%	$51.0747	$51.07	$51.05	$51.10
Purchase #3	$60.88	9.623%	$66.7385	$66.74	$66.75	$66.70
Purchase #4	$112.65	7.303%	$120.8768	$120.88	$120.90	$120.90
Purchase #5	$90.73	12.299%	$101.8889	$101.89	$101.90	$101.90
Purchase #6	$225.91	8.242%	$244.5295	$244.53	$244.55	$244.50
Purchase #7	$190.52	12.765%	$214.8399	$214.84	$214.85	$214.80
7 purchase totals =	$768.89		$846.3370	$846.34	$846.40	$846.30