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	$244.57	10.604%	$270.5042	$270.50	$270.50	$270.50
Purchase #2	$126.42	11.401%	$140.8331	$140.83	$140.85	$140.80
Purchase #3	$99.35	13.275%	$112.5387	$112.54	$112.55	$112.50
Purchase #4	$80.63	10.236%	$88.8833	$88.88	$88.90	$88.90
Purchase #5	$143.35	13.197%	$162.2679	$162.27	$162.25	$162.30
Purchase #6	$18.52	8.408%	$20.0772	$20.08	$20.10	$20.10
Purchase #7	$75.71	11.466%	$84.3909	$84.39	$84.40	$84.40
7 purchase totals =	$788.55		$879.4953	$879.49	$879.55	$879.50