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	$47.75	9.612%	$52.3397	$52.34	$52.35	$52.30
Purchase #2	$20.37	3.656%	$21.1147	$21.11	$21.10	$21.10
Purchase #3	$142.35	5.359%	$149.9785	$149.98	$150.00	$150.00
Purchase #4	$143.37	5.232%	$150.8711	$150.87	$150.85	$150.90
Purchase #5	$181.98	4.342%	$189.8816	$189.88	$189.90	$189.90
Purchase #6	$33.56	10.838%	$37.1972	$37.20	$37.20	$37.20
Purchase #7	$108.43	3.271%	$111.9767	$111.98	$112.00	$112.00
7 purchase totals =	$677.81		$713.3595	$713.36	$713.40	$713.40