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	$203.30	9.590%	$222.7965	$222.80	$222.80	$222.80
Purchase #2	$126.74	13.383%	$143.7016	$143.70	$143.70	$143.70
Purchase #3	$138.25	3.798%	$143.5007	$143.50	$143.50	$143.50
Purchase #4	$33.96	9.655%	$37.2388	$37.24	$37.25	$37.20
Purchase #5	$127.33	9.278%	$139.1437	$139.14	$139.15	$139.10
Purchase #6	$172.53	11.219%	$191.8861	$191.89	$191.90	$191.90
Purchase #7	$48.75	10.114%	$53.6806	$53.68	$53.70	$53.70
7 purchase totals =	$850.86		$931.9480	$931.95	$932.00	$931.90