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	$216.40	8.266%	$234.2876	$234.29	$234.30	$234.30
Purchase #2	$115.42	12.416%	$129.7505	$129.75	$129.75	$129.80
Purchase #3	$204.89	9.428%	$224.207	$224.21	$224.20	$224.20
Purchase #4	$242.70	5.311%	$255.5898	$255.59	$255.60	$255.60
Purchase #5	$116.75	5.800%	$123.5215	$123.52	$123.50	$123.50
Purchase #6	$96.54	13.248%	$109.3296	$109.33	$109.35	$109.30
Purchase #7	$128.28	13.133%	$145.127	$145.13	$145.15	$145.10
7 purchase totals =	$1,120.98		$1,221.8130	$1,221.82	$1,221.85	$1,221.80