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	$99.77	4.232%	$103.9923	$103.99	$104.00	$104.00
Purchase #2	$16.90	7.257%	$18.1264	$18.13	$18.15	$18.10
Purchase #3	$120.62	11.499%	$134.4901	$134.49	$134.50	$134.50
Purchase #4	$18.49	7.665%	$19.9073	$19.91	$19.90	$19.90
Purchase #5	$29.83	12.510%	$33.5617	$33.56	$33.55	$33.60
Purchase #6	$196.65	13.437%	$223.0739	$223.07	$223.05	$223.10
Purchase #7	$58.89	13.869%	$67.0575	$67.06	$67.05	$67.10
7 purchase totals =	$541.15		$600.2092	$600.21	$600.20	$600.30