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	$79.88	10.379%	$88.1707	$88.17	$88.15	$88.20
Purchase #2	$150.96	6.175%	$160.2818	$160.28	$160.30	$160.30
Purchase #3	$132.34	7.790%	$142.6493	$142.65	$142.65	$142.60
Purchase #4	$40.72	12.454%	$45.7913	$45.79	$45.80	$45.80
Purchase #5	$23.46	5.591%	$24.7716	$24.77	$24.75	$24.80
Purchase #6	$74.32	10.158%	$81.8694	$81.87	$81.85	$81.90
Purchase #7	$55.52	10.723%	$61.4734	$61.47	$61.45	$61.50
7 purchase totals =	$557.20		$605.0075	$605.00	$604.95	$605.10