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	$227.48	12.145%	$255.1074	$255.11	$255.10	$255.10
Purchase #2	$200.30	4.656%	$209.626	$209.63	$209.65	$209.60
Purchase #3	$90.87	10.716%	$100.6076	$100.61	$100.60	$100.60
Purchase #4	$175.45	7.764%	$189.0719	$189.07	$189.05	$189.10
Purchase #5	$16.76	10.592%	$18.5352	$18.54	$18.55	$18.50
Purchase #6	$7.33	9.791%	$8.0477	$8.05	$8.05	$8.00
Purchase #7	$54.52	12.752%	$61.4724	$61.47	$61.45	$61.50
7 purchase totals =	$772.71		$842.4682	$842.48	$842.45	$842.40