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	$29.81	5.636%	$31.4901	$31.49	$31.50	$31.50
Purchase #2	$60.25	12.479%	$67.7686	$67.77	$67.75	$67.80
Purchase #3	$190.72	11.525%	$212.7005	$212.70	$212.70	$212.70
Purchase #4	$37.95	3.579%	$39.3082	$39.31	$39.30	$39.30
Purchase #5	$188.50	4.294%	$196.5942	$196.59	$196.60	$196.60
Purchase #6	$144.48	8.135%	$156.2334	$156.23	$156.25	$156.20
Purchase #7	$238.88	8.604%	$259.4332	$259.43	$259.45	$259.40
7 purchase totals =	$890.59		$963.5282	$963.52	$963.55	$963.50