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	$50.44	7.307%	$54.1257	$54.13	$54.15	$54.10
Purchase #2	$245.54	4.691%	$257.0583	$257.06	$257.05	$257.10
Purchase #3	$82.64	7.717%	$89.0173	$89.02	$89.00	$89.00
Purchase #4	$224.60	5.457%	$236.8564	$236.86	$236.85	$236.90
Purchase #5	$51.63	9.640%	$56.6071	$56.61	$56.60	$56.60
Purchase #6	$55.69	10.356%	$61.4573	$61.46	$61.45	$61.50
Purchase #7	$109.46	8.722%	$119.0071	$119.01	$119.00	$119.00
7 purchase totals =	$820.00		$874.1292	$874.15	$874.10	$874.20