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	$7.89	11.862%	$8.8259	$8.83	$8.85	$8.80
Purchase #2	$13.40	12.384%	$15.0595	$15.06	$15.05	$15.10
Purchase #3	$135.85	6.362%	$144.4928	$144.49	$144.50	$144.50
Purchase #4	$115.82	7.482%	$124.4857	$124.49	$124.50	$124.50
Purchase #5	$149.51	10.709%	$165.521	$165.52	$165.50	$165.50
Purchase #6	$12.30	9.258%	$13.4387	$13.44	$13.45	$13.40
Purchase #7	$150.72	7.570%	$162.1295	$162.13	$162.15	$162.10
7 purchase totals =	$585.49		$633.9531	$633.96	$634.00	$633.90