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	$184.34	3.187%	$190.2149	$190.21	$190.20	$190.20
Purchase #2	$161.32	3.434%	$166.8597	$166.86	$166.85	$166.90
Purchase #3	$139.61	4.421%	$145.7822	$145.78	$145.80	$145.80
Purchase #4	$209.64	6.501%	$223.2687	$223.27	$223.25	$223.30
Purchase #5	$238.97	3.671%	$247.7426	$247.74	$247.75	$247.70
Purchase #6	$174.83	12.652%	$196.9495	$196.95	$196.95	$196.90
Purchase #7	$229.50	13.663%	$260.8566	$260.86	$260.85	$260.90
7 purchase totals =	$1,338.21		$1,431.6742	$1,431.67	$1,431.65	$1,431.70