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	$78.72	4.804%	$82.5017	$82.50	$82.50	$82.50
Purchase #2	$5.30	10.638%	$5.8638	$5.86	$5.85	$5.90
Purchase #3	$45.91	9.834%	$50.4248	$50.42	$50.40	$50.40
Purchase #4	$212.40	13.516%	$241.108	$241.11	$241.10	$241.10
Purchase #5	$232.34	12.373%	$261.0874	$261.09	$261.10	$261.10
Purchase #6	$100.70	4.380%	$105.1107	$105.11	$105.10	$105.10
Purchase #7	$171.54	7.515%	$184.4312	$184.43	$184.45	$184.40
7 purchase totals =	$846.91		$930.5276	$930.52	$930.50	$930.50