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	$73.55	12.627%	$82.8372	$82.84	$82.85	$82.80
Purchase #2	$118.42	11.658%	$132.2254	$132.23	$132.25	$132.20
Purchase #3	$67.81	3.618%	$70.2634	$70.26	$70.25	$70.30
Purchase #4	$24.57	4.152%	$25.5901	$25.59	$25.60	$25.60
Purchase #5	$38.51	4.733%	$40.3327	$40.33	$40.35	$40.30
Purchase #6	$36.34	8.456%	$39.4129	$39.41	$39.40	$39.40
Purchase #7	$20.28	5.833%	$21.4629	$21.46	$21.45	$21.50
7 purchase totals =	$379.48		$412.1246	$412.12	$412.15	$412.10