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	$92.72	7.431%	$99.61	$99.61	$99.60	$99.60
Purchase #2	$118.69	10.592%	$131.2616	$131.26	$131.25	$131.30
Purchase #3	$237.99	5.377%	$250.7867	$250.79	$250.80	$250.80
Purchase #4	$94.34	5.206%	$99.2513	$99.25	$99.25	$99.30
Purchase #5	$150.81	10.583%	$166.7702	$166.77	$166.75	$166.80
Purchase #6	$170.60	8.725%	$185.4849	$185.48	$185.50	$185.50
Purchase #7	$47.90	3.545%	$49.5981	$49.60	$49.60	$49.60
7 purchase totals =	$913.05		$982.7628	$982.76	$982.75	$982.90