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	$26.29	9.654%	$28.828	$28.83	$28.85	$28.80
Purchase #2	$145.67	3.753%	$151.137	$151.14	$151.15	$151.10
Purchase #3	$222.59	5.698%	$235.2732	$235.27	$235.25	$235.30
Purchase #4	$150.80	6.349%	$160.3743	$160.37	$160.35	$160.40
Purchase #5	$57.46	10.319%	$63.3893	$63.39	$63.40	$63.40
Purchase #6	$86.43	3.659%	$89.5925	$89.59	$89.60	$89.60
Purchase #7	$190.36	12.152%	$213.4925	$213.49	$213.50	$213.50
7 purchase totals =	$879.60		$942.0868	$942.08	$942.10	$942.10