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	$140.29	4.583%	$146.7195	$146.72	$146.70	$146.70
Purchase #2	$18.43	7.314%	$19.778	$19.78	$19.80	$19.80
Purchase #3	$168.61	4.304%	$175.867	$175.87	$175.85	$175.90
Purchase #4	$118.89	9.662%	$130.3772	$130.38	$130.40	$130.40
Purchase #5	$23.59	7.570%	$25.3758	$25.38	$25.40	$25.40
Purchase #6	$56.56	4.811%	$59.2811	$59.28	$59.30	$59.30
Purchase #7	$111.80	12.310%	$125.5626	$125.56	$125.55	$125.60
7 purchase totals =	$638.17		$682.9612	$682.97	$683.00	$683.10