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	$243.87	7.721%	$262.6992	$262.70	$262.70	$262.70
Purchase #2	$85.42	6.423%	$90.9065	$90.91	$90.90	$90.90
Purchase #3	$41.46	10.316%	$45.737	$45.74	$45.75	$45.70
Purchase #4	$94.84	13.596%	$107.7344	$107.73	$107.75	$107.70
Purchase #5	$152.92	11.827%	$171.0058	$171.01	$171.00	$171.00
Purchase #6	$129.78	3.390%	$134.1795	$134.18	$134.20	$134.20
Purchase #7	$162.27	3.612%	$168.1312	$168.13	$168.15	$168.10
7 purchase totals =	$910.56		$980.3936	$980.40	$980.45	$980.30