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	$128.99	7.524%	$138.6952	$138.70	$138.70	$138.70
Purchase #2	$206.32	6.368%	$219.4585	$219.46	$219.45	$219.50
Purchase #3	$123.66	7.534%	$132.9765	$132.98	$133.00	$133.00
Purchase #4	$188.88	6.123%	$200.4451	$200.45	$200.45	$200.40
Purchase #5	$89.75	11.722%	$100.2705	$100.27	$100.25	$100.30
Purchase #6	$162.69	3.776%	$168.8332	$168.83	$168.85	$168.80
Purchase #7	$106.37	3.289%	$109.8685	$109.87	$109.85	$109.90
7 purchase totals =	$1,006.66		$1,070.5475	$1,070.56	$1,070.55	$1,070.60