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	$82.64	8.182%	$89.4016	$89.40	$89.40	$89.40
Purchase #2	$230.60	12.114%	$258.5349	$258.53	$258.55	$258.50
Purchase #3	$47.74	8.654%	$51.8714	$51.87	$51.85	$51.90
Purchase #4	$139.62	11.842%	$156.1538	$156.15	$156.15	$156.20
Purchase #5	$162.48	12.302%	$182.4683	$182.47	$182.45	$182.50
Purchase #6	$42.43	11.469%	$47.2963	$47.30	$47.30	$47.30
Purchase #7	$141.89	11.873%	$158.7366	$158.74	$158.75	$158.70
7 purchase totals =	$847.40		$944.4629	$944.46	$944.45	$944.50