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	$72.36	8.580%	$78.5685	$78.57	$78.55	$78.60
Purchase #2	$184.79	3.559%	$191.3667	$191.37	$191.35	$191.40
Purchase #3	$12.78	7.320%	$13.7155	$13.72	$13.70	$13.70
Purchase #4	$184.95	10.642%	$204.6324	$204.63	$204.65	$204.60
Purchase #5	$82.88	9.333%	$90.6152	$90.62	$90.60	$90.60
Purchase #6	$89.99	12.805%	$101.5132	$101.51	$101.50	$101.50
Purchase #7	$12.26	9.461%	$13.4199	$13.42	$13.40	$13.40
7 purchase totals =	$640.01		$693.8314	$693.84	$693.75	$693.80