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	$178.59	6.144%	$189.5626	$189.56	$189.55	$189.60
Purchase #2	$146.99	6.213%	$156.1225	$156.12	$156.10	$156.10
Purchase #3	$178.84	9.806%	$196.3771	$196.38	$196.40	$196.40
Purchase #4	$59.33	11.711%	$66.2781	$66.28	$66.30	$66.30
Purchase #5	$94.40	9.710%	$103.5662	$103.57	$103.55	$103.60
Purchase #6	$140.80	8.352%	$152.5596	$152.56	$152.55	$152.60
Purchase #7	$129.82	8.639%	$141.0351	$141.04	$141.05	$141.00
7 purchase totals =	$928.77		$1,005.5012	$1,005.51	$1,005.50	$1,005.60