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	$11.94	3.119%	$12.3124	$12.31	$12.30	$12.30
Purchase #2	$126.59	4.108%	$131.7903	$131.79	$131.80	$131.80
Purchase #3	$84.63	4.522%	$88.457	$88.46	$88.45	$88.50
Purchase #4	$131.41	9.605%	$144.0319	$144.03	$144.05	$144.00
Purchase #5	$170.87	12.164%	$191.6546	$191.65	$191.65	$191.70
Purchase #6	$67.79	5.354%	$71.4195	$71.42	$71.40	$71.40
Purchase #7	$50.98	8.658%	$55.3938	$55.39	$55.40	$55.40
7 purchase totals =	$644.21		$695.0595	$695.05	$695.05	$695.10