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	$128.72	6.573%	$137.1808	$137.18	$137.20	$137.20
Purchase #2	$8.63	11.110%	$9.5888	$9.59	$9.60	$9.60
Purchase #3	$211.70	5.245%	$222.8037	$222.80	$222.80	$222.80
Purchase #4	$154.56	8.382%	$167.5152	$167.52	$167.50	$167.50
Purchase #5	$146.77	12.448%	$165.0399	$165.04	$165.05	$165.00
Purchase #6	$28.93	10.113%	$31.8557	$31.86	$31.85	$31.90
Purchase #7	$232.46	9.194%	$253.8324	$253.83	$253.85	$253.80
7 purchase totals =	$911.77		$987.8165	$987.82	$987.85	$987.80