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	$51.33	5.429%	$54.1167	$54.12	$54.10	$54.10
Purchase #2	$99.46	6.622%	$106.0462	$106.05	$106.05	$106.00
Purchase #3	$133.52	10.367%	$147.362	$147.36	$147.35	$147.40
Purchase #4	$157.32	7.694%	$169.4242	$169.42	$169.40	$169.40
Purchase #5	$40.70	7.145%	$43.608	$43.61	$43.60	$43.60
Purchase #6	$245.50	3.267%	$253.5205	$253.52	$253.50	$253.50
Purchase #7	$215.64	4.373%	$225.0699	$225.07	$225.05	$225.10
7 purchase totals =	$943.47		$999.1475	$999.15	$999.05	$999.10