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	$87.89	13.626%	$99.8659	$99.87	$99.85	$99.90
Purchase #2	$83.74	3.270%	$86.4783	$86.48	$86.50	$86.50
Purchase #3	$30.86	4.305%	$32.1885	$32.19	$32.20	$32.20
Purchase #4	$11.52	3.147%	$11.8825	$11.88	$11.90	$11.90
Purchase #5	$155.60	13.694%	$176.9079	$176.91	$176.90	$176.90
Purchase #6	$51.62	11.847%	$57.7354	$57.74	$57.75	$57.70
Purchase #7	$88.34	4.280%	$92.121	$92.12	$92.10	$92.10
7 purchase totals =	$509.57		$557.1795	$557.19	$557.20	$557.20