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	$80.47	10.539%	$88.9507	$88.95	$88.95	$89.00
Purchase #2	$228.94	10.856%	$253.7937	$253.79	$253.80	$253.80
Purchase #3	$10.94	11.774%	$12.2281	$12.23	$12.25	$12.20
Purchase #4	$209.95	13.849%	$239.026	$239.03	$239.05	$239.00
Purchase #5	$37.57	8.730%	$40.8499	$40.85	$40.85	$40.80
Purchase #6	$96.31	9.474%	$105.4344	$105.43	$105.45	$105.40
Purchase #7	$127.98	11.145%	$142.2434	$142.24	$142.25	$142.20
7 purchase totals =	$792.16		$882.5262	$882.52	$882.60	$882.40