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	$111.60	10.521%	$123.3414	$123.34	$123.35	$123.30
Purchase #2	$82.48	8.642%	$89.6079	$89.61	$89.60	$89.60
Purchase #3	$132.63	13.116%	$150.0258	$150.03	$150.05	$150.00
Purchase #4	$227.54	13.144%	$257.4479	$257.45	$257.45	$257.40
Purchase #5	$191.39	10.542%	$211.5663	$211.57	$211.55	$211.60
Purchase #6	$246.61	9.705%	$270.5435	$270.54	$270.55	$270.50
Purchase #7	$30.90	10.429%	$34.1226	$34.12	$34.10	$34.10
7 purchase totals =	$1,023.15		$1,136.6554	$1,136.66	$1,136.65	$1,136.50