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	$40.46	6.541%	$43.1065	$43.11	$43.10	$43.10
Purchase #2	$151.95	12.790%	$171.3844	$171.38	$171.40	$171.40
Purchase #3	$30.46	7.624%	$32.7823	$32.78	$32.80	$32.80
Purchase #4	$90.56	9.623%	$99.2746	$99.27	$99.25	$99.30
Purchase #5	$176.47	4.831%	$184.9953	$185.00	$185.00	$185.00
Purchase #6	$215.62	10.866%	$239.0493	$239.05	$239.05	$239.00
Purchase #7	$53.60	11.119%	$59.5598	$59.56	$59.55	$59.60
7 purchase totals =	$759.12		$830.1522	$830.15	$830.15	$830.20