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	$14.57	6.669%	$15.5417	$15.54	$15.55	$15.50
Purchase #2	$56.63	9.573%	$62.0512	$62.05	$62.05	$62.10
Purchase #3	$203.75	9.742%	$223.5993	$223.60	$223.60	$223.60
Purchase #4	$119.65	6.190%	$127.0563	$127.06	$127.05	$127.10
Purchase #5	$106.62	4.108%	$110.9999	$111.00	$111.00	$111.00
Purchase #6	$33.42	12.238%	$37.5099	$37.51	$37.50	$37.50
Purchase #7	$82.68	10.561%	$91.4118	$91.41	$91.40	$91.40
7 purchase totals =	$617.32		$668.1701	$668.17	$668.15	$668.20