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	$80.36	10.793%	$89.0333	$89.03	$89.05	$89.00
Purchase #2	$160.27	6.406%	$170.5369	$170.54	$170.55	$170.50
Purchase #3	$52.42	3.533%	$54.272	$54.27	$54.25	$54.30
Purchase #4	$229.34	10.326%	$253.0216	$253.02	$253.00	$253.00
Purchase #5	$125.76	13.539%	$142.7866	$142.79	$142.80	$142.80
Purchase #6	$208.27	12.650%	$234.6162	$234.62	$234.60	$234.60
Purchase #7	$46.51	3.855%	$48.303	$48.30	$48.30	$48.30
7 purchase totals =	$902.93		$992.5696	$992.57	$992.55	$992.50