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	$80.66	10.488%	$89.1196	$89.12	$89.10	$89.10
Purchase #2	$172.47	9.846%	$189.4514	$189.45	$189.45	$189.50
Purchase #3	$73.35	4.557%	$76.6926	$76.69	$76.70	$76.70
Purchase #4	$172.47	11.372%	$192.0833	$192.08	$192.10	$192.10
Purchase #5	$48.42	10.748%	$53.6242	$53.62	$53.60	$53.60
Purchase #6	$50.28	10.708%	$55.664	$55.66	$55.65	$55.70
Purchase #7	$153.73	4.609%	$160.8154	$160.82	$160.80	$160.80
7 purchase totals =	$751.38		$817.4505	$817.44	$817.40	$817.50