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	$212.78	8.652%	$231.1897	$231.19	$231.20	$231.20
Purchase #2	$28.45	11.867%	$31.8262	$31.83	$31.85	$31.80
Purchase #3	$129.49	12.841%	$146.1178	$146.12	$146.10	$146.10
Purchase #4	$100.71	8.755%	$109.5272	$109.53	$109.55	$109.50
Purchase #5	$60.90	6.320%	$64.7489	$64.75	$64.75	$64.70
Purchase #6	$106.52	5.700%	$112.5916	$112.59	$112.60	$112.60
Purchase #7	$80.89	13.378%	$91.7115	$91.71	$91.70	$91.70
7 purchase totals =	$719.74		$787.7129	$787.72	$787.75	$787.60