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	$157.44	9.551%	$172.4771	$172.48	$172.50	$172.50
Purchase #2	$238.25	11.855%	$266.4945	$266.49	$266.50	$266.50
Purchase #3	$28.29	4.144%	$29.4623	$29.46	$29.45	$29.50
Purchase #4	$143.65	9.158%	$156.8055	$156.81	$156.80	$156.80
Purchase #5	$83.52	9.582%	$91.5229	$91.52	$91.50	$91.50
Purchase #6	$147.74	9.670%	$162.0265	$162.03	$162.05	$162.00
Purchase #7	$27.63	6.809%	$29.5113	$29.51	$29.50	$29.50
7 purchase totals =	$826.52		$908.3001	$908.30	$908.30	$908.30