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	$231.65	3.730%	$240.2905	$240.29	$240.30	$240.30
Purchase #2	$157.97	10.749%	$174.9502	$174.95	$174.95	$175.00
Purchase #3	$126.69	10.320%	$139.7644	$139.76	$139.75	$139.80
Purchase #4	$106.52	7.271%	$114.2651	$114.27	$114.25	$114.30
Purchase #5	$196.40	10.208%	$216.4485	$216.45	$216.45	$216.40
Purchase #6	$215.64	3.473%	$223.1292	$223.13	$223.15	$223.10
Purchase #7	$100.89	10.725%	$111.7105	$111.71	$111.70	$111.70
7 purchase totals =	$1,135.76		$1,220.5584	$1,220.56	$1,220.55	$1,220.60