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	$100.55	4.835%	$105.4116	$105.41	$105.40	$105.40
Purchase #2	$73.91	6.482%	$78.7008	$78.70	$78.70	$78.70
Purchase #3	$159.49	6.623%	$170.053	$170.05	$170.05	$170.10
Purchase #4	$173.76	12.187%	$194.9361	$194.94	$194.95	$194.90
Purchase #5	$212.71	4.662%	$222.6265	$222.63	$222.65	$222.60
Purchase #6	$27.73	3.732%	$28.7649	$28.76	$28.75	$28.80
Purchase #7	$70.87	10.854%	$78.5622	$78.56	$78.55	$78.60
7 purchase totals =	$819.02		$879.0551	$879.05	$879.05	$879.10