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	$187.45	5.669%	$198.0765	$198.08	$198.10	$198.10
Purchase #2	$102.51	10.447%	$113.2192	$113.22	$113.20	$113.20
Purchase #3	$104.51	13.479%	$118.5969	$118.60	$118.60	$118.60
Purchase #4	$93.25	7.519%	$100.2615	$100.26	$100.25	$100.30
Purchase #5	$111.74	10.694%	$123.6895	$123.69	$123.70	$123.70
Purchase #6	$78.31	8.863%	$85.2506	$85.25	$85.25	$85.30
Purchase #7	$72.87	12.816%	$82.209	$82.21	$82.20	$82.20
7 purchase totals =	$750.64		$821.3032	$821.31	$821.30	$821.40