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	$78.60	6.503%	$83.7114	$83.71	$83.70	$83.70
Purchase #2	$5.93	10.116%	$6.5299	$6.53	$6.55	$6.50
Purchase #3	$212.59	7.831%	$229.2379	$229.24	$229.25	$229.20
Purchase #4	$78.59	4.655%	$82.2484	$82.25	$82.25	$82.20
Purchase #5	$225.25	9.826%	$247.3831	$247.38	$247.40	$247.40
Purchase #6	$39.38	12.720%	$44.3891	$44.39	$44.40	$44.40
Purchase #7	$85.86	5.389%	$90.487	$90.49	$90.50	$90.50
7 purchase totals =	$726.20		$783.9868	$783.99	$784.05	$783.90