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	$245.59	11.748%	$274.4419	$274.44	$274.45	$274.40
Purchase #2	$199.74	12.190%	$224.0883	$224.09	$224.10	$224.10
Purchase #3	$122.47	3.803%	$127.1275	$127.13	$127.15	$127.10
Purchase #4	$149.30	11.614%	$166.6397	$166.64	$166.65	$166.60
Purchase #5	$233.96	13.696%	$266.0032	$266.00	$266.00	$266.00
Purchase #6	$72.80	7.792%	$78.4726	$78.47	$78.45	$78.50
Purchase #7	$102.31	4.363%	$106.7738	$106.77	$106.75	$106.80
7 purchase totals =	$1,126.17		$1,243.5470	$1,243.54	$1,243.55	$1,243.50