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	$110.36	11.535%	$123.09	$123.09	$123.10	$123.10
Purchase #2	$226.60	6.494%	$241.3154	$241.32	$241.30	$241.30
Purchase #3	$210.32	7.154%	$225.3663	$225.37	$225.35	$225.40
Purchase #4	$48.58	12.381%	$54.5947	$54.59	$54.60	$54.60
Purchase #5	$27.43	3.831%	$28.4808	$28.48	$28.50	$28.50
Purchase #6	$54.30	12.855%	$61.2803	$61.28	$61.30	$61.30
Purchase #7	$26.58	11.203%	$29.5578	$29.56	$29.55	$29.60
7 purchase totals =	$704.17		$763.6853	$763.69	$763.70	$763.80