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	$249.27	12.112%	$279.4616	$279.46	$279.45	$279.50
Purchase #2	$215.44	3.718%	$223.4501	$223.45	$223.45	$223.50
Purchase #3	$115.36	11.693%	$128.849	$128.85	$128.85	$128.80
Purchase #4	$150.48	9.565%	$164.8734	$164.87	$164.85	$164.90
Purchase #5	$56.36	3.415%	$58.2847	$58.28	$58.30	$58.30
Purchase #6	$38.32	9.652%	$42.0186	$42.02	$42.00	$42.00
Purchase #7	$130.97	13.106%	$148.1349	$148.13	$148.15	$148.10
7 purchase totals =	$956.20		$1,045.0723	$1,045.06	$1,045.05	$1,045.10