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	$19.76	3.426%	$20.437	$20.44	$20.45	$20.40
Purchase #2	$188.68	9.689%	$206.9612	$206.96	$206.95	$207.00
Purchase #3	$159.85	9.419%	$174.9063	$174.91	$174.90	$174.90
Purchase #4	$238.87	6.246%	$253.7898	$253.79	$253.80	$253.80
Purchase #5	$79.96	11.386%	$89.0642	$89.06	$89.05	$89.10
Purchase #6	$7.28	13.341%	$8.2512	$8.25	$8.25	$8.30
Purchase #7	$87.45	3.491%	$90.5029	$90.50	$90.50	$90.50
7 purchase totals =	$781.85		$843.9126	$843.91	$843.90	$844.00