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	$135.60	4.494%	$141.6939	$141.69	$141.70	$141.70
Purchase #2	$153.52	7.479%	$165.0018	$165.00	$165.00	$165.00
Purchase #3	$81.38	6.831%	$86.9391	$86.94	$86.95	$86.90
Purchase #4	$82.39	9.415%	$90.147	$90.15	$90.15	$90.10
Purchase #5	$92.93	7.681%	$100.068	$100.07	$100.05	$100.10
Purchase #6	$103.43	4.636%	$108.225	$108.23	$108.25	$108.20
Purchase #7	$175.71	5.486%	$185.3495	$185.35	$185.35	$185.30
7 purchase totals =	$824.96		$877.4243	$877.43	$877.45	$877.30