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	$40.27	4.599%	$42.122	$42.12	$42.10	$42.10
Purchase #2	$228.76	7.291%	$245.4389	$245.44	$245.45	$245.40
Purchase #3	$39.56	7.190%	$42.4044	$42.40	$42.40	$42.40
Purchase #4	$242.78	6.188%	$257.8032	$257.80	$257.80	$257.80
Purchase #5	$31.60	6.152%	$33.544	$33.54	$33.55	$33.50
Purchase #6	$16.72	10.397%	$18.4584	$18.46	$18.45	$18.50
Purchase #7	$58.53	8.274%	$63.3728	$63.37	$63.35	$63.40
7 purchase totals =	$658.22		$703.1437	$703.13	$703.10	$703.10