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	$189.26	5.830%	$200.2939	$200.29	$200.30	$200.30
Purchase #2	$144.57	12.178%	$162.1757	$162.18	$162.20	$162.20
Purchase #3	$39.73	9.740%	$43.5997	$43.60	$43.60	$43.60
Purchase #4	$51.78	4.415%	$54.0661	$54.07	$54.05	$54.10
Purchase #5	$95.78	6.451%	$101.9588	$101.96	$101.95	$102.00
Purchase #6	$104.69	6.869%	$111.8812	$111.88	$111.90	$111.90
Purchase #7	$118.88	7.645%	$127.9684	$127.97	$127.95	$128.00
7 purchase totals =	$744.69		$801.9438	$801.95	$801.95	$802.10