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	$81.87	11.316%	$91.1344	$91.13	$91.15	$91.10
Purchase #2	$18.89	7.383%	$20.2846	$20.28	$20.30	$20.30
Purchase #3	$67.87	12.835%	$76.5811	$76.58	$76.60	$76.60
Purchase #4	$48.28	9.850%	$53.0356	$53.04	$53.05	$53.00
Purchase #5	$216.58	9.285%	$236.6895	$236.69	$236.70	$236.70
Purchase #6	$223.85	7.490%	$240.6164	$240.62	$240.60	$240.60
Purchase #7	$74.49	5.803%	$78.8127	$78.81	$78.80	$78.80
7 purchase totals =	$731.83		$797.1543	$797.15	$797.20	$797.10