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	$54.40	9.499%	$59.5675	$59.57	$59.55	$59.60
Purchase #2	$162.51	10.491%	$179.5589	$179.56	$179.55	$179.60
Purchase #3	$207.89	12.846%	$234.5955	$234.60	$234.60	$234.60
Purchase #4	$213.59	9.590%	$234.0733	$234.07	$234.05	$234.10
Purchase #5	$99.26	9.353%	$108.5438	$108.54	$108.55	$108.50
Purchase #6	$16.73	8.317%	$18.1214	$18.12	$18.10	$18.10
Purchase #7	$223.88	13.834%	$254.8516	$254.85	$254.85	$254.90
7 purchase totals =	$978.26		$1,089.3120	$1,089.31	$1,089.25	$1,089.40