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	$164.48	12.653%	$185.2917	$185.29	$185.30	$185.30
Purchase #2	$46.45	11.824%	$51.9422	$51.94	$51.95	$51.90
Purchase #3	$47.80	3.596%	$49.5189	$49.52	$49.50	$49.50
Purchase #4	$32.28	4.531%	$33.7426	$33.74	$33.75	$33.70
Purchase #5	$74.32	7.499%	$79.8933	$79.89	$79.90	$79.90
Purchase #6	$225.31	6.369%	$239.66	$239.66	$239.65	$239.70
Purchase #7	$128.59	11.126%	$142.8969	$142.90	$142.90	$142.90
7 purchase totals =	$719.23		$782.9456	$782.94	$782.95	$782.90