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	$17.53	7.367%	$18.8214	$18.82	$18.80	$18.80
Purchase #2	$130.74	9.353%	$142.9681	$142.97	$142.95	$143.00
Purchase #3	$79.74	11.253%	$88.7131	$88.71	$88.70	$88.70
Purchase #4	$211.41	5.574%	$223.194	$223.19	$223.20	$223.20
Purchase #5	$71.83	13.590%	$81.5917	$81.59	$81.60	$81.60
Purchase #6	$17.32	6.270%	$18.406	$18.41	$18.40	$18.40
Purchase #7	$171.27	11.414%	$190.8188	$190.82	$190.80	$190.80
7 purchase totals =	$699.84		$764.5131	$764.51	$764.45	$764.50