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	$234.25	11.786%	$261.8587	$261.86	$261.85	$261.90
Purchase #2	$38.32	11.756%	$42.8249	$42.82	$42.80	$42.80
Purchase #3	$19.84	4.314%	$20.6959	$20.70	$20.70	$20.70
Purchase #4	$117.73	5.117%	$123.7542	$123.75	$123.75	$123.80
Purchase #5	$16.46	8.392%	$17.8413	$17.84	$17.85	$17.80
Purchase #6	$224.27	9.447%	$245.4568	$245.46	$245.45	$245.50
Purchase #7	$71.44	9.544%	$78.2582	$78.26	$78.25	$78.30
7 purchase totals =	$722.31		$790.6900	$790.69	$790.65	$790.80