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	$232.73	7.779%	$250.8341	$250.83	$250.85	$250.80
Purchase #2	$22.76	7.314%	$24.4247	$24.42	$24.40	$24.40
Purchase #3	$6.27	13.573%	$7.121	$7.12	$7.10	$7.10
Purchase #4	$132.69	6.703%	$141.5842	$141.58	$141.60	$141.60
Purchase #5	$52.28	4.718%	$54.7466	$54.75	$54.75	$54.70
Purchase #6	$70.98	13.379%	$80.4764	$80.48	$80.50	$80.50
Purchase #7	$23.85	13.443%	$27.0562	$27.06	$27.05	$27.10
7 purchase totals =	$541.56		$586.2432	$586.24	$586.25	$586.20