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	$74.76	12.131%	$83.8291	$83.83	$83.85	$83.80
Purchase #2	$35.60	4.428%	$37.1764	$37.18	$37.20	$37.20
Purchase #3	$212.80	3.307%	$219.8373	$219.84	$219.85	$219.80
Purchase #4	$117.38	3.772%	$121.8076	$121.81	$121.80	$121.80
Purchase #5	$200.61	7.480%	$215.6156	$215.62	$215.60	$215.60
Purchase #6	$125.41	13.337%	$142.1359	$142.14	$142.15	$142.10
Purchase #7	$226.64	12.450%	$254.8567	$254.86	$254.85	$254.90
7 purchase totals =	$993.20		$1,075.2586	$1,075.28	$1,075.30	$1,075.20