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	$39.29	9.286%	$42.9385	$42.94	$42.95	$42.90
Purchase #2	$154.31	13.144%	$174.5925	$174.59	$174.60	$174.60
Purchase #3	$137.67	13.242%	$155.9003	$155.90	$155.90	$155.90
Purchase #4	$74.82	7.111%	$80.1405	$80.14	$80.15	$80.10
Purchase #5	$88.31	5.200%	$92.9021	$92.90	$92.90	$92.90
Purchase #6	$6.96	11.460%	$7.7576	$7.76	$7.75	$7.80
Purchase #7	$211.55	8.873%	$230.3208	$230.32	$230.30	$230.30
7 purchase totals =	$712.91		$784.5523	$784.55	$784.55	$784.50