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	$229.80	9.105%	$250.7233	$250.72	$250.70	$250.70
Purchase #2	$178.33	7.620%	$191.9187	$191.92	$191.90	$191.90
Purchase #3	$76.51	5.349%	$80.6025	$80.60	$80.60	$80.60
Purchase #4	$182.51	3.690%	$189.2446	$189.24	$189.25	$189.20
Purchase #5	$89.53	10.476%	$98.9092	$98.91	$98.90	$98.90
Purchase #6	$211.72	4.324%	$220.8748	$220.87	$220.85	$220.90
Purchase #7	$105.83	5.497%	$111.6475	$111.65	$111.65	$111.60
7 purchase totals =	$1,074.23		$1,143.9206	$1,143.91	$1,143.85	$1,143.80