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	$17.36	11.672%	$19.3863	$19.39	$19.40	$19.40
Purchase #2	$196.75	3.723%	$204.075	$204.08	$204.10	$204.10
Purchase #3	$134.85	5.473%	$142.2303	$142.23	$142.25	$142.20
Purchase #4	$131.98	7.385%	$141.7267	$141.73	$141.75	$141.70
Purchase #5	$65.52	12.216%	$73.5239	$73.52	$73.50	$73.50
Purchase #6	$209.30	10.791%	$231.8856	$231.89	$231.90	$231.90
Purchase #7	$63.38	11.297%	$70.54	$70.54	$70.55	$70.50
7 purchase totals =	$819.14		$883.3678	$883.38	$883.45	$883.30