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	$152.51	8.281%	$165.1394	$165.14	$165.15	$165.10
Purchase #2	$40.48	5.304%	$42.6271	$42.63	$42.65	$42.60
Purchase #3	$79.54	12.795%	$89.7171	$89.72	$89.70	$89.70
Purchase #4	$168.30	8.845%	$183.1861	$183.19	$183.20	$183.20
Purchase #5	$20.51	3.608%	$21.25	$21.25	$21.25	$21.30
Purchase #6	$16.36	13.830%	$18.6226	$18.62	$18.60	$18.60
Purchase #7	$39.83	12.755%	$44.9103	$44.91	$44.90	$44.90
7 purchase totals =	$517.53		$565.4526	$565.46	$565.45	$565.40