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	$250.40	11.668%	$279.6167	$279.62	$279.60	$279.60
Purchase #2	$18.84	11.781%	$21.0595	$21.06	$21.05	$21.10
Purchase #3	$71.86	7.205%	$77.0375	$77.04	$77.05	$77.00
Purchase #4	$174.79	6.328%	$185.8507	$185.85	$185.85	$185.90
Purchase #5	$93.87	12.626%	$105.722	$105.72	$105.70	$105.70
Purchase #6	$119.41	9.775%	$131.0823	$131.08	$131.10	$131.10
Purchase #7	$99.40	4.228%	$103.6026	$103.60	$103.60	$103.60
7 purchase totals =	$828.57		$903.9713	$903.97	$903.95	$904.00