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	$80.64	9.604%	$88.3847	$88.38	$88.40	$88.40
Purchase #2	$194.28	13.117%	$219.7637	$219.76	$219.75	$219.80
Purchase #3	$73.86	5.734%	$78.0951	$78.10	$78.10	$78.10
Purchase #4	$96.99	3.424%	$100.3109	$100.31	$100.30	$100.30
Purchase #5	$20.60	6.257%	$21.8889	$21.89	$21.90	$21.90
Purchase #6	$89.66	5.413%	$94.5133	$94.51	$94.50	$94.50
Purchase #7	$27.46	11.482%	$30.613	$30.61	$30.60	$30.60
7 purchase totals =	$583.49		$633.5696	$633.56	$633.55	$633.60