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	$9.51	10.869%	$10.5436	$10.54	$10.55	$10.50
Purchase #2	$242.50	3.722%	$251.5259	$251.53	$251.55	$251.50
Purchase #3	$16.52	3.802%	$17.1481	$17.15	$17.15	$17.10
Purchase #4	$143.25	8.517%	$155.4506	$155.45	$155.45	$155.50
Purchase #5	$234.30	8.469%	$254.1429	$254.14	$254.15	$254.10
Purchase #6	$61.42	9.271%	$67.1142	$67.11	$67.10	$67.10
Purchase #7	$242.45	4.543%	$253.4645	$253.46	$253.45	$253.50
7 purchase totals =	$949.95		$1,009.3898	$1,009.38	$1,009.40	$1,009.30