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	$96.77	8.579%	$105.0719	$105.07	$105.05	$105.10
Purchase #2	$60.82	12.516%	$68.4322	$68.43	$68.45	$68.40
Purchase #3	$42.47	13.790%	$48.3266	$48.33	$48.35	$48.30
Purchase #4	$113.99	8.519%	$123.7008	$123.70	$123.70	$123.70
Purchase #5	$85.68	12.768%	$96.6196	$96.62	$96.60	$96.60
Purchase #6	$39.31	7.616%	$42.3038	$42.30	$42.30	$42.30
Purchase #7	$159.90	7.511%	$171.9101	$171.91	$171.90	$171.90
7 purchase totals =	$598.94		$656.3650	$656.36	$656.35	$656.30