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	$115.95	12.559%	$130.5122	$130.51	$130.50	$130.50
Purchase #2	$100.43	3.541%	$103.9862	$103.99	$104.00	$104.00
Purchase #3	$233.52	7.796%	$251.7252	$251.73	$251.75	$251.70
Purchase #4	$171.64	6.379%	$182.5889	$182.59	$182.60	$182.60
Purchase #5	$170.40	12.382%	$191.4989	$191.50	$191.50	$191.50
Purchase #6	$89.51	10.316%	$98.7439	$98.74	$98.75	$98.70
Purchase #7	$37.95	13.204%	$42.9609	$42.96	$42.95	$43.00
7 purchase totals =	$919.40		$1,002.0162	$1,002.02	$1,002.05	$1,002.00