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	$170.69	4.507%	$178.383	$178.38	$178.40	$178.40
Purchase #2	$200.54	10.644%	$221.8855	$221.89	$221.90	$221.90
Purchase #3	$68.36	4.142%	$71.1915	$71.19	$71.20	$71.20
Purchase #4	$127.69	10.239%	$140.7642	$140.76	$140.75	$140.80
Purchase #5	$61.75	12.527%	$69.4854	$69.49	$69.50	$69.50
Purchase #6	$50.26	8.782%	$54.6738	$54.67	$54.65	$54.70
Purchase #7	$48.47	6.435%	$51.589	$51.59	$51.60	$51.60
7 purchase totals =	$727.76		$787.9724	$787.97	$788.00	$788.10