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	$25.91	9.565%	$28.3883	$28.39	$28.40	$28.40
Purchase #2	$107.36	11.423%	$119.6237	$119.62	$119.60	$119.60
Purchase #3	$80.45	11.377%	$89.6028	$89.60	$89.60	$89.60
Purchase #4	$68.92	11.773%	$77.034	$77.03	$77.05	$77.00
Purchase #5	$243.51	5.261%	$256.3211	$256.32	$256.30	$256.30
Purchase #6	$113.78	10.396%	$125.6086	$125.61	$125.60	$125.60
Purchase #7	$199.88	13.478%	$226.8198	$226.82	$226.80	$226.80
7 purchase totals =	$839.81		$923.3983	$923.39	$923.35	$923.30