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	$173.28	7.268%	$185.874	$185.87	$185.85	$185.90
Purchase #2	$115.77	12.658%	$130.4242	$130.42	$130.40	$130.40
Purchase #3	$97.59	10.601%	$107.9355	$107.94	$107.95	$107.90
Purchase #4	$213.70	11.384%	$238.0276	$238.03	$238.05	$238.00
Purchase #5	$31.38	7.772%	$33.8189	$33.82	$33.80	$33.80
Purchase #6	$59.67	13.589%	$67.7786	$67.78	$67.80	$67.80
Purchase #7	$144.71	13.816%	$164.7031	$164.70	$164.70	$164.70
7 purchase totals =	$836.10		$928.5619	$928.56	$928.55	$928.50