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	$46.42	6.168%	$49.2832	$49.28	$49.30	$49.30
Purchase #2	$134.25	12.173%	$150.5923	$150.59	$150.60	$150.60
Purchase #3	$240.46	3.838%	$249.6889	$249.69	$249.70	$249.70
Purchase #4	$181.57	13.807%	$206.6394	$206.64	$206.65	$206.60
Purchase #5	$177.58	8.110%	$191.9817	$191.98	$192.00	$192.00
Purchase #6	$91.85	8.664%	$99.8079	$99.81	$99.80	$99.80
Purchase #7	$136.45	11.737%	$152.4651	$152.47	$152.45	$152.50
7 purchase totals =	$1,008.58		$1,100.4585	$1,100.46	$1,100.50	$1,100.50