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	$79.86	4.396%	$83.3706	$83.37	$83.35	$83.40
Purchase #2	$114.81	4.685%	$120.1888	$120.19	$120.20	$120.20
Purchase #3	$145.45	9.594%	$159.4045	$159.40	$159.40	$159.40
Purchase #4	$99.85	3.594%	$103.4386	$103.44	$103.45	$103.40
Purchase #5	$245.77	13.834%	$279.7698	$279.77	$279.75	$279.80
Purchase #6	$173.98	12.760%	$196.1798	$196.18	$196.20	$196.20
Purchase #7	$70.83	3.514%	$73.319	$73.32	$73.30	$73.30
7 purchase totals =	$930.55		$1,015.6711	$1,015.67	$1,015.65	$1,015.70