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	$63.62	10.688%	$70.4197	$70.42	$70.40	$70.40
Purchase #2	$191.61	10.572%	$211.867	$211.87	$211.85	$211.90
Purchase #3	$174.39	3.466%	$180.4344	$180.43	$180.45	$180.40
Purchase #4	$73.54	6.757%	$78.5091	$78.51	$78.50	$78.50
Purchase #5	$23.30	10.810%	$25.8187	$25.82	$25.80	$25.80
Purchase #6	$57.78	4.600%	$60.4379	$60.44	$60.45	$60.40
Purchase #7	$135.56	4.726%	$141.9666	$141.97	$141.95	$142.00
7 purchase totals =	$719.80		$769.4534	$769.46	$769.40	$769.40