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	$54.80	11.572%	$61.1415	$61.14	$61.15	$61.10
Purchase #2	$123.41	3.588%	$127.838	$127.84	$127.85	$127.80
Purchase #3	$85.50	5.860%	$90.5103	$90.51	$90.50	$90.50
Purchase #4	$101.84	7.207%	$109.1796	$109.18	$109.20	$109.20
Purchase #5	$204.56	4.589%	$213.9473	$213.95	$213.95	$213.90
Purchase #6	$79.73	3.662%	$82.6497	$82.65	$82.65	$82.60
Purchase #7	$151.57	4.592%	$158.5301	$158.53	$158.55	$158.50
7 purchase totals =	$801.41		$843.7965	$843.80	$843.85	$843.60