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	$79.71	11.386%	$88.7858	$88.79	$88.80	$88.80
Purchase #2	$115.58	9.218%	$126.2342	$126.23	$126.25	$126.20
Purchase #3	$24.69	10.628%	$27.3141	$27.31	$27.30	$27.30
Purchase #4	$94.44	12.145%	$105.9097	$105.91	$105.90	$105.90
Purchase #5	$139.79	11.699%	$156.144	$156.14	$156.15	$156.10
Purchase #6	$99.60	10.459%	$110.0172	$110.02	$110.00	$110.00
Purchase #7	$30.47	5.519%	$32.1516	$32.15	$32.15	$32.20
7 purchase totals =	$584.28		$646.5566	$646.55	$646.55	$646.50