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	$91.82	9.860%	$100.8735	$100.87	$100.85	$100.90
Purchase #2	$57.76	13.872%	$65.7725	$65.77	$65.75	$65.80
Purchase #3	$250.62	7.548%	$269.5368	$269.54	$269.55	$269.50
Purchase #4	$169.26	6.437%	$180.1553	$180.16	$180.15	$180.20
Purchase #5	$77.34	10.472%	$85.439	$85.44	$85.45	$85.40
Purchase #6	$250.52	11.759%	$279.9786	$279.98	$280.00	$280.00
Purchase #7	$104.61	4.292%	$109.0999	$109.10	$109.10	$109.10
7 purchase totals =	$1,001.93		$1,090.8556	$1,090.86	$1,090.85	$1,090.90