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	$151.77	13.434%	$172.1588	$172.16	$172.15	$172.20
Purchase #2	$93.90	10.349%	$103.6177	$103.62	$103.60	$103.60
Purchase #3	$39.58	8.273%	$42.8545	$42.85	$42.85	$42.90
Purchase #4	$31.75	4.365%	$33.1359	$33.14	$33.15	$33.10
Purchase #5	$228.94	6.156%	$243.0335	$243.03	$243.05	$243.00
Purchase #6	$6.62	3.187%	$6.831	$6.83	$6.85	$6.80
Purchase #7	$91.42	11.444%	$101.8821	$101.88	$101.90	$101.90
7 purchase totals =	$643.98		$703.5135	$703.51	$703.55	$703.50