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	$127.58	8.414%	$138.3146	$138.31	$138.30	$138.30
Purchase #2	$161.85	6.833%	$172.9092	$172.91	$172.90	$172.90
Purchase #3	$175.38	9.367%	$191.8078	$191.81	$191.80	$191.80
Purchase #4	$93.34	3.756%	$96.8459	$96.85	$96.85	$96.80
Purchase #5	$182.26	5.239%	$191.8086	$191.81	$191.80	$191.80
Purchase #6	$104.96	6.391%	$111.668	$111.67	$111.65	$111.70
Purchase #7	$144.72	9.108%	$157.9011	$157.90	$157.90	$157.90
7 purchase totals =	$990.09		$1,061.2552	$1,061.26	$1,061.20	$1,061.20