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	$63.30	13.515%	$71.855	$71.86	$71.85	$71.90
Purchase #2	$163.27	12.657%	$183.9351	$183.94	$183.95	$183.90
Purchase #3	$128.81	6.666%	$137.3965	$137.40	$137.40	$137.40
Purchase #4	$217.37	10.527%	$240.2525	$240.25	$240.25	$240.30
Purchase #5	$111.76	10.331%	$123.3059	$123.31	$123.30	$123.30
Purchase #6	$142.80	11.385%	$159.0578	$159.06	$159.05	$159.10
Purchase #7	$62.64	4.261%	$65.3091	$65.31	$65.30	$65.30
7 purchase totals =	$889.95		$981.1119	$981.13	$981.10	$981.20