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	$28.47	3.126%	$29.36	$29.36	$29.35	$29.40
Purchase #2	$168.52	13.364%	$191.041	$191.04	$191.05	$191.00
Purchase #3	$91.88	9.635%	$100.7326	$100.73	$100.75	$100.70
Purchase #4	$42.45	6.708%	$45.2975	$45.30	$45.30	$45.30
Purchase #5	$209.36	8.487%	$227.1284	$227.13	$227.15	$227.10
Purchase #6	$211.54	9.553%	$231.7484	$231.75	$231.75	$231.70
Purchase #7	$127.80	13.645%	$145.2383	$145.24	$145.25	$145.20
7 purchase totals =	$880.02		$970.5462	$970.55	$970.60	$970.40