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	$249.70	11.121%	$277.4691	$277.47	$277.45	$277.50
Purchase #2	$51.65	5.574%	$54.529	$54.53	$54.55	$54.50
Purchase #3	$65.40	11.155%	$72.6954	$72.70	$72.70	$72.70
Purchase #4	$78.85	4.816%	$82.6474	$82.65	$82.65	$82.60
Purchase #5	$94.58	7.840%	$101.9951	$102.00	$102.00	$102.00
Purchase #6	$168.86	9.765%	$185.3492	$185.35	$185.35	$185.30
Purchase #7	$122.60	12.827%	$138.3259	$138.33	$138.35	$138.30
7 purchase totals =	$831.64		$913.0111	$913.03	$913.05	$912.90