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	$122.64	11.121%	$136.2788	$136.28	$136.30	$136.30
Purchase #2	$246.78	7.254%	$264.6814	$264.68	$264.70	$264.70
Purchase #3	$30.51	9.739%	$33.4814	$33.48	$33.50	$33.50
Purchase #4	$50.85	5.268%	$53.5288	$53.53	$53.55	$53.50
Purchase #5	$78.88	6.222%	$83.7879	$83.79	$83.80	$83.80
Purchase #6	$51.26	6.111%	$54.3925	$54.39	$54.40	$54.40
Purchase #7	$35.88	7.493%	$38.5685	$38.57	$38.55	$38.60
7 purchase totals =	$616.80		$664.7193	$664.72	$664.80	$664.80