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	$81.64	13.241%	$92.45	$92.45	$92.45	$92.50
Purchase #2	$147.55	3.310%	$152.4339	$152.43	$152.45	$152.40
Purchase #3	$24.31	12.798%	$27.4212	$27.42	$27.40	$27.40
Purchase #4	$6.93	7.366%	$7.4405	$7.44	$7.45	$7.40
Purchase #5	$241.47	4.761%	$252.9664	$252.97	$252.95	$253.00
Purchase #6	$215.92	3.443%	$223.3541	$223.35	$223.35	$223.40
Purchase #7	$100.79	4.308%	$105.132	$105.13	$105.15	$105.10
7 purchase totals =	$818.61		$861.1981	$861.19	$861.20	$861.20