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	$144.49	9.612%	$158.3784	$158.38	$158.40	$158.40
Purchase #2	$46.80	6.327%	$49.761	$49.76	$49.75	$49.80
Purchase #3	$228.28	6.820%	$243.8487	$243.85	$243.85	$243.80
Purchase #4	$171.67	6.380%	$182.6225	$182.62	$182.60	$182.60
Purchase #5	$38.71	3.292%	$39.9843	$39.98	$40.00	$40.00
Purchase #6	$59.52	13.113%	$67.3249	$67.32	$67.30	$67.30
Purchase #7	$210.55	12.425%	$236.7108	$236.71	$236.70	$236.70
7 purchase totals =	$900.02		$978.6306	$978.62	$978.60	$978.60