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	$115.82	11.366%	$128.9841	$128.98	$129.00	$129.00
Purchase #2	$92.76	11.585%	$103.5062	$103.51	$103.50	$103.50
Purchase #3	$38.86	8.606%	$42.2043	$42.20	$42.20	$42.20
Purchase #4	$246.47	13.310%	$279.2752	$279.28	$279.30	$279.30
Purchase #5	$42.31	8.657%	$45.9728	$45.97	$45.95	$46.00
Purchase #6	$66.56	8.389%	$72.1437	$72.14	$72.15	$72.10
Purchase #7	$168.84	12.372%	$189.7289	$189.73	$189.75	$189.70
7 purchase totals =	$771.62		$861.8152	$861.81	$861.85	$861.80