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	$10.64	9.353%	$11.6352	$11.64	$11.65	$11.60
Purchase #2	$180.56	9.814%	$198.2802	$198.28	$198.30	$198.30
Purchase #3	$131.36	6.755%	$140.2334	$140.23	$140.25	$140.20
Purchase #4	$117.71	8.302%	$127.4823	$127.48	$127.50	$127.50
Purchase #5	$18.48	11.372%	$20.5815	$20.58	$20.60	$20.60
Purchase #6	$94.88	6.333%	$100.8888	$100.89	$100.90	$100.90
Purchase #7	$223.62	8.200%	$241.9568	$241.96	$241.95	$242.00
7 purchase totals =	$777.25		$841.0582	$841.06	$841.15	$841.10