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	$105.49	6.105%	$111.9302	$111.93	$111.95	$111.90
Purchase #2	$111.65	11.427%	$124.4082	$124.41	$124.40	$124.40
Purchase #3	$90.52	13.744%	$102.9611	$102.96	$102.95	$103.00
Purchase #4	$158.68	9.870%	$174.3417	$174.34	$174.35	$174.30
Purchase #5	$30.77	9.605%	$33.7255	$33.73	$33.75	$33.70
Purchase #6	$118.44	9.266%	$129.4147	$129.41	$129.40	$129.40
Purchase #7	$90.97	13.577%	$103.321	$103.32	$103.30	$103.30
7 purchase totals =	$706.52		$780.1024	$780.10	$780.10	$780.00