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	$164.28	6.464%	$174.8991	$174.90	$174.90	$174.90
Purchase #2	$210.94	13.253%	$238.8959	$238.90	$238.90	$238.90
Purchase #3	$233.30	9.319%	$255.0412	$255.04	$255.05	$255.00
Purchase #4	$80.25	7.291%	$86.101	$86.10	$86.10	$86.10
Purchase #5	$70.78	4.865%	$74.2234	$74.22	$74.20	$74.20
Purchase #6	$37.40	5.226%	$39.3545	$39.35	$39.35	$39.40
Purchase #7	$55.70	12.770%	$62.8129	$62.81	$62.80	$62.80
7 purchase totals =	$852.65		$931.3280	$931.32	$931.30	$931.30