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	$235.31	12.198%	$264.0131	$264.01	$264.00	$264.00
Purchase #2	$65.69	4.323%	$68.5298	$68.53	$68.55	$68.50
Purchase #3	$176.92	6.287%	$188.043	$188.04	$188.05	$188.00
Purchase #4	$179.40	9.683%	$196.7713	$196.77	$196.75	$196.80
Purchase #5	$111.54	10.514%	$123.2673	$123.27	$123.25	$123.30
Purchase #6	$59.92	5.552%	$63.2468	$63.25	$63.25	$63.20
Purchase #7	$61.40	5.555%	$64.8108	$64.81	$64.80	$64.80
7 purchase totals =	$890.18		$968.6821	$968.68	$968.65	$968.60