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	$99.85	10.560%	$110.3942	$110.39	$110.40	$110.40
Purchase #2	$96.62	8.761%	$105.0849	$105.08	$105.10	$105.10
Purchase #3	$46.33	12.371%	$52.0615	$52.06	$52.05	$52.10
Purchase #4	$190.91	9.699%	$209.4264	$209.43	$209.45	$209.40
Purchase #5	$31.89	7.121%	$34.1609	$34.16	$34.15	$34.20
Purchase #6	$53.40	6.623%	$56.9367	$56.94	$56.95	$56.90
Purchase #7	$124.35	5.534%	$131.2315	$131.23	$131.25	$131.20
7 purchase totals =	$643.35		$699.2961	$699.29	$699.35	$699.30