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	$76.88	7.698%	$82.7982	$82.80	$82.80	$82.80
Purchase #2	$114.89	11.281%	$127.8507	$127.85	$127.85	$127.90
Purchase #3	$87.79	8.578%	$95.3206	$95.32	$95.30	$95.30
Purchase #4	$5.84	12.246%	$6.5552	$6.56	$6.55	$6.60
Purchase #5	$72.74	10.861%	$80.6403	$80.64	$80.65	$80.60
Purchase #6	$244.69	8.814%	$266.257	$266.26	$266.25	$266.30
Purchase #7	$134.97	7.528%	$145.1305	$145.13	$145.15	$145.10
7 purchase totals =	$737.80		$804.5525	$804.56	$804.55	$804.60