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	$27.86	3.609%	$28.8655	$28.87	$28.85	$28.90
Purchase #2	$81.50	9.704%	$89.4088	$89.41	$89.40	$89.40
Purchase #3	$246.50	7.297%	$264.4871	$264.49	$264.50	$264.50
Purchase #4	$39.99	6.303%	$42.5106	$42.51	$42.50	$42.50
Purchase #5	$9.56	5.422%	$10.0783	$10.08	$10.10	$10.10
Purchase #6	$192.32	10.720%	$212.9367	$212.94	$212.95	$212.90
Purchase #7	$174.43	11.253%	$194.0586	$194.06	$194.05	$194.10
7 purchase totals =	$772.16		$842.3456	$842.36	$842.35	$842.40