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	$27.97	7.478%	$30.0616	$30.06	$30.05	$30.10
Purchase #2	$53.33	6.566%	$56.8316	$56.83	$56.85	$56.80
Purchase #3	$60.98	7.377%	$65.4785	$65.48	$65.50	$65.50
Purchase #4	$246.60	5.647%	$260.5255	$260.53	$260.55	$260.50
Purchase #5	$136.72	6.137%	$145.1105	$145.11	$145.10	$145.10
Purchase #6	$36.47	3.697%	$37.8183	$37.82	$37.80	$37.80
Purchase #7	$115.63	10.349%	$127.5965	$127.60	$127.60	$127.60
7 purchase totals =	$677.70		$723.4225	$723.43	$723.45	$723.40