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	$223.99	7.162%	$240.0322	$240.03	$240.05	$240.00
Purchase #2	$86.25	4.396%	$90.0416	$90.04	$90.05	$90.00
Purchase #3	$146.89	12.623%	$165.4319	$165.43	$165.45	$165.40
Purchase #4	$19.73	5.863%	$20.8868	$20.89	$20.90	$20.90
Purchase #5	$114.73	13.168%	$129.8376	$129.84	$129.85	$129.80
Purchase #6	$134.76	6.648%	$143.7188	$143.72	$143.70	$143.70
Purchase #7	$32.32	3.117%	$33.3274	$33.33	$33.35	$33.30
7 purchase totals =	$758.67		$823.2763	$823.28	$823.35	$823.10