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	$78.56	5.286%	$82.7127	$82.71	$82.70	$82.70
Purchase #2	$65.56	5.709%	$69.3028	$69.30	$69.30	$69.30
Purchase #3	$224.59	4.618%	$234.9616	$234.96	$234.95	$235.00
Purchase #4	$61.54	6.388%	$65.4712	$65.47	$65.45	$65.50
Purchase #5	$221.52	4.221%	$230.8704	$230.87	$230.85	$230.90
Purchase #6	$106.72	4.829%	$111.8735	$111.87	$111.85	$111.90
Purchase #7	$170.99	6.860%	$182.7199	$182.72	$182.70	$182.70
7 purchase totals =	$929.48		$977.9121	$977.90	$977.80	$978.00