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	$230.90	5.206%	$242.9207	$242.92	$242.90	$242.90
Purchase #2	$166.32	12.208%	$186.6243	$186.62	$186.60	$186.60
Purchase #3	$76.65	11.464%	$85.4372	$85.44	$85.45	$85.40
Purchase #4	$200.27	11.874%	$224.0501	$224.05	$224.05	$224.10
Purchase #5	$47.46	6.297%	$50.4486	$50.45	$50.45	$50.40
Purchase #6	$109.26	13.435%	$123.9391	$123.94	$123.95	$123.90
Purchase #7	$23.25	9.717%	$25.5092	$25.51	$25.50	$25.50
7 purchase totals =	$854.11		$938.9292	$938.93	$938.90	$938.80