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	$240.91	9.237%	$263.1629	$263.16	$263.15	$263.20
Purchase #2	$84.50	7.290%	$90.6601	$90.66	$90.65	$90.70
Purchase #3	$245.50	6.537%	$261.5483	$261.55	$261.55	$261.50
Purchase #4	$215.54	12.215%	$241.8682	$241.87	$241.85	$241.90
Purchase #5	$123.42	6.218%	$131.0943	$131.09	$131.10	$131.10
Purchase #6	$67.66	5.429%	$71.3333	$71.33	$71.35	$71.30
Purchase #7	$34.87	4.514%	$36.444	$36.44	$36.45	$36.40
7 purchase totals =	$1,012.40		$1,096.1111	$1,096.10	$1,096.10	$1,096.10