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	$54.59	9.623%	$59.8432	$59.84	$59.85	$59.80
Purchase #2	$34.35	13.250%	$38.9014	$38.90	$38.90	$38.90
Purchase #3	$6.76	8.661%	$7.3455	$7.35	$7.35	$7.30
Purchase #4	$58.94	4.467%	$61.5728	$61.57	$61.55	$61.60
Purchase #5	$91.91	9.225%	$100.3887	$100.39	$100.40	$100.40
Purchase #6	$212.76	13.380%	$241.2273	$241.23	$241.25	$241.20
Purchase #7	$68.56	9.406%	$75.0088	$75.01	$75.00	$75.00
7 purchase totals =	$527.87		$584.2877	$584.29	$584.30	$584.20