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	$46.61	7.628%	$50.1654	$50.17	$50.15	$50.20
Purchase #2	$61.81	9.386%	$67.6115	$67.61	$67.60	$67.60
Purchase #3	$228.82	11.700%	$255.5919	$255.59	$255.60	$255.60
Purchase #4	$163.71	6.330%	$174.0728	$174.07	$174.05	$174.10
Purchase #5	$96.81	3.793%	$100.482	$100.48	$100.50	$100.50
Purchase #6	$240.54	6.468%	$256.0981	$256.10	$256.10	$256.10
Purchase #7	$105.84	8.627%	$114.9708	$114.97	$114.95	$115.00
7 purchase totals =	$944.14		$1,018.9925	$1,018.99	$1,018.95	$1,019.10