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	$17.96	6.460%	$19.1202	$19.12	$19.10	$19.10
Purchase #2	$220.78	10.842%	$244.717	$244.72	$244.70	$244.70
Purchase #3	$72.88	10.379%	$80.4442	$80.44	$80.45	$80.40
Purchase #4	$243.83	13.564%	$276.9031	$276.90	$276.90	$276.90
Purchase #5	$93.83	10.342%	$103.5339	$103.53	$103.55	$103.50
Purchase #6	$44.61	13.752%	$50.7448	$50.74	$50.75	$50.70
Purchase #7	$205.40	10.654%	$227.2833	$227.28	$227.30	$227.30
7 purchase totals =	$899.29		$1,002.7465	$1,002.73	$1,002.75	$1,002.60