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	$57.82	5.704%	$61.1181	$61.12	$61.10	$61.10
Purchase #2	$185.70	7.715%	$200.0268	$200.03	$200.05	$200.00
Purchase #3	$244.90	12.698%	$275.9974	$276.00	$276.00	$276.00
Purchase #4	$68.90	3.667%	$71.4266	$71.43	$71.45	$71.40
Purchase #5	$46.42	10.108%	$51.1121	$51.11	$51.10	$51.10
Purchase #6	$105.25	3.177%	$108.5938	$108.59	$108.60	$108.60
Purchase #7	$55.89	7.862%	$60.2841	$60.28	$60.30	$60.30
7 purchase totals =	$764.88		$828.5589	$828.56	$828.60	$828.50