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	$236.86	8.382%	$256.7136	$256.71	$256.70	$256.70
Purchase #2	$170.62	7.150%	$182.8193	$182.82	$182.80	$182.80
Purchase #3	$49.92	10.523%	$55.1731	$55.17	$55.15	$55.20
Purchase #4	$179.35	3.437%	$185.5143	$185.51	$185.50	$185.50
Purchase #5	$102.76	6.584%	$109.5257	$109.53	$109.55	$109.50
Purchase #6	$104.86	9.710%	$115.0419	$115.04	$115.05	$115.00
Purchase #7	$45.38	13.429%	$51.4741	$51.47	$51.45	$51.50
7 purchase totals =	$889.75		$956.2620	$956.25	$956.20	$956.20