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	$73.55	10.468%	$81.2492	$81.25	$81.25	$81.20
Purchase #2	$223.44	11.740%	$249.6719	$249.67	$249.65	$249.70
Purchase #3	$120.88	9.698%	$132.6029	$132.60	$132.60	$132.60
Purchase #4	$173.45	5.250%	$182.5561	$182.56	$182.55	$182.60
Purchase #5	$167.32	12.274%	$187.8569	$187.86	$187.85	$187.90
Purchase #6	$51.53	7.422%	$55.3546	$55.35	$55.35	$55.40
Purchase #7	$128.89	13.873%	$146.7709	$146.77	$146.75	$146.80
7 purchase totals =	$939.06		$1,036.0625	$1,036.06	$1,036.00	$1,036.20