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	$153.94	12.768%	$173.5951	$173.60	$173.60	$173.60
Purchase #2	$108.44	7.728%	$116.8202	$116.82	$116.80	$116.80
Purchase #3	$100.31	6.345%	$106.6747	$106.67	$106.65	$106.70
Purchase #4	$83.33	7.552%	$89.6231	$89.62	$89.60	$89.60
Purchase #5	$190.47	7.838%	$205.399	$205.40	$205.40	$205.40
Purchase #6	$242.99	11.252%	$270.3312	$270.33	$270.35	$270.30
Purchase #7	$61.67	6.177%	$65.4794	$65.48	$65.50	$65.50
7 purchase totals =	$941.15		$1,027.9227	$1,027.92	$1,027.90	$1,027.90