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	$145.98	6.337%	$155.2308	$155.23	$155.25	$155.20
Purchase #2	$146.82	5.474%	$154.8569	$154.86	$154.85	$154.90
Purchase #3	$39.91	6.810%	$42.6279	$42.63	$42.65	$42.60
Purchase #4	$72.88	8.566%	$79.1229	$79.12	$79.10	$79.10
Purchase #5	$55.41	13.707%	$63.005	$63.01	$63.00	$63.00
Purchase #6	$84.63	5.654%	$89.415	$89.42	$89.40	$89.40
Purchase #7	$97.82	8.792%	$106.4203	$106.42	$106.40	$106.40
7 purchase totals =	$643.45		$690.6788	$690.69	$690.65	$690.60