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	$90.27	3.256%	$93.2092	$93.21	$93.20	$93.20
Purchase #2	$126.34	8.342%	$136.8793	$136.88	$136.90	$136.90
Purchase #3	$103.31	5.422%	$108.9115	$108.91	$108.90	$108.90
Purchase #4	$48.71	8.632%	$52.9146	$52.91	$52.90	$52.90
Purchase #5	$59.78	7.515%	$64.2725	$64.27	$64.25	$64.30
Purchase #6	$120.92	4.707%	$126.6117	$126.61	$126.60	$126.60
Purchase #7	$94.96	5.135%	$99.8362	$99.84	$99.85	$99.80
7 purchase totals =	$644.29		$682.6350	$682.63	$682.60	$682.60