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	$167.33	6.756%	$178.6348	$178.63	$178.65	$178.60
Purchase #2	$228.65	11.168%	$254.1856	$254.19	$254.20	$254.20
Purchase #3	$175.41	8.326%	$190.0146	$190.01	$190.00	$190.00
Purchase #4	$112.69	9.652%	$123.5668	$123.57	$123.55	$123.60
Purchase #5	$53.35	4.692%	$55.8532	$55.85	$55.85	$55.90
Purchase #6	$29.58	5.286%	$31.1436	$31.14	$31.15	$31.10
Purchase #7	$84.57	5.766%	$89.4463	$89.45	$89.45	$89.40
7 purchase totals =	$851.58		$922.8449	$922.84	$922.85	$922.80