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	$7.59	7.271%	$8.1419	$8.14	$8.15	$8.10
Purchase #2	$55.41	11.490%	$61.7766	$61.78	$61.80	$61.80
Purchase #3	$9.89	3.637%	$10.2497	$10.25	$10.25	$10.20
Purchase #4	$14.56	13.677%	$16.5514	$16.55	$16.55	$16.60
Purchase #5	$239.97	13.134%	$271.4877	$271.49	$271.50	$271.50
Purchase #6	$61.43	11.399%	$68.4324	$68.43	$68.45	$68.40
Purchase #7	$56.42	5.396%	$59.4644	$59.46	$59.45	$59.50
7 purchase totals =	$445.27		$496.1041	$496.10	$496.15	$496.10