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	$33.44	10.799%	$37.0512	$37.05	$37.05	$37.10
Purchase #2	$122.30	9.870%	$134.371	$134.37	$134.35	$134.40
Purchase #3	$219.39	4.559%	$229.392	$229.39	$229.40	$229.40
Purchase #4	$30.59	8.758%	$33.2691	$33.27	$33.25	$33.30
Purchase #5	$43.82	11.506%	$48.8619	$48.86	$48.85	$48.90
Purchase #6	$96.73	5.692%	$102.2359	$102.24	$102.25	$102.20
Purchase #7	$223.55	5.380%	$235.577	$235.58	$235.60	$235.60
7 purchase totals =	$769.82		$820.7581	$820.76	$820.75	$820.90