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	$242.46	4.850%	$254.2193	$254.22	$254.20	$254.20
Purchase #2	$58.98	12.712%	$66.4775	$66.48	$66.50	$66.50
Purchase #3	$25.45	12.363%	$28.5964	$28.60	$28.60	$28.60
Purchase #4	$242.45	5.202%	$255.0622	$255.06	$255.05	$255.10
Purchase #5	$120.52	5.689%	$127.3764	$127.38	$127.40	$127.40
Purchase #6	$64.27	5.349%	$67.7078	$67.71	$67.70	$67.70
Purchase #7	$30.82	8.307%	$33.3802	$33.38	$33.40	$33.40
7 purchase totals =	$784.95		$832.8198	$832.83	$832.85	$832.90