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	$175.45	7.337%	$188.3228	$188.32	$188.30	$188.30
Purchase #2	$75.72	3.332%	$78.243	$78.24	$78.25	$78.20
Purchase #3	$160.68	8.685%	$174.6351	$174.64	$174.65	$174.60
Purchase #4	$83.25	11.723%	$93.0094	$93.01	$93.00	$93.00
Purchase #5	$214.72	6.618%	$228.9302	$228.93	$228.95	$228.90
Purchase #6	$78.39	5.839%	$82.9672	$82.97	$82.95	$83.00
Purchase #7	$19.88	3.109%	$20.4981	$20.50	$20.50	$20.50
7 purchase totals =	$808.09		$866.6058	$866.61	$866.60	$866.50