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	$25.83	6.204%	$27.4325	$27.43	$27.45	$27.40
Purchase #2	$70.41	11.814%	$78.7282	$78.73	$78.75	$78.70
Purchase #3	$109.81	5.436%	$115.7793	$115.78	$115.80	$115.80
Purchase #4	$142.50	8.159%	$154.1266	$154.13	$154.15	$154.10
Purchase #5	$116.99	8.635%	$127.0921	$127.09	$127.10	$127.10
Purchase #6	$172.31	11.846%	$192.7218	$192.72	$192.70	$192.70
Purchase #7	$64.82	8.818%	$70.5358	$70.54	$70.55	$70.50
7 purchase totals =	$702.67		$766.4163	$766.42	$766.50	$766.30