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	$74.82	4.109%	$77.8944	$77.89	$77.90	$77.90
Purchase #2	$202.28	4.606%	$211.597	$211.60	$211.60	$211.60
Purchase #3	$157.72	5.672%	$166.6659	$166.67	$166.65	$166.70
Purchase #4	$211.96	10.335%	$233.8661	$233.87	$233.85	$233.90
Purchase #5	$186.34	13.473%	$211.4456	$211.45	$211.45	$211.40
Purchase #6	$52.38	3.821%	$54.3814	$54.38	$54.40	$54.40
Purchase #7	$163.85	7.197%	$175.6423	$175.64	$175.65	$175.60
7 purchase totals =	$1,049.35		$1,131.4927	$1,131.50	$1,131.50	$1,131.50