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	$201.72	9.744%	$221.3756	$221.38	$221.40	$221.40
Purchase #2	$135.55	4.446%	$141.5766	$141.58	$141.60	$141.60
Purchase #3	$230.68	3.529%	$238.8207	$238.82	$238.80	$238.80
Purchase #4	$47.42	13.595%	$53.8667	$53.87	$53.85	$53.90
Purchase #5	$71.49	12.104%	$80.1431	$80.14	$80.15	$80.10
Purchase #6	$61.29	10.338%	$67.6262	$67.63	$67.65	$67.60
Purchase #7	$19.73	4.859%	$20.6887	$20.69	$20.70	$20.70
7 purchase totals =	$767.88		$824.0976	$824.11	$824.15	$824.10