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	$47.40	7.773%	$51.0844	$51.08	$51.10	$51.10
Purchase #2	$147.39	7.534%	$158.4944	$158.49	$158.50	$158.50
Purchase #3	$191.32	4.711%	$200.3331	$200.33	$200.35	$200.30
Purchase #4	$94.52	9.286%	$103.2971	$103.30	$103.30	$103.30
Purchase #5	$51.44	11.618%	$57.4163	$57.42	$57.40	$57.40
Purchase #6	$101.43	7.660%	$109.1995	$109.20	$109.20	$109.20
Purchase #7	$223.83	3.607%	$231.9035	$231.90	$231.90	$231.90
7 purchase totals =	$857.33		$911.7283	$911.72	$911.75	$911.70