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	$89.44	3.672%	$92.7242	$92.72	$92.70	$92.70
Purchase #2	$227.88	13.577%	$258.8193	$258.82	$258.80	$258.80
Purchase #3	$156.30	6.789%	$166.9112	$166.91	$166.90	$166.90
Purchase #4	$189.83	7.279%	$203.6477	$203.65	$203.65	$203.60
Purchase #5	$132.76	7.569%	$142.8086	$142.81	$142.80	$142.80
Purchase #6	$220.83	4.140%	$229.9724	$229.97	$229.95	$230.00
Purchase #7	$167.35	10.631%	$185.141	$185.14	$185.15	$185.10
7 purchase totals =	$1,184.39		$1,280.0244	$1,280.02	$1,279.95	$1,279.90